fcM . f*f< ,-**. y* K: f 1 v - r^ S. W CMRISTY. hfcSB BE \ tice, it must be admitted that the pursuit of this branch of chemistry to any satisfactory purpose, requires, notwithstanding, considerable expen- diture of time. I would therefore advise every one desirous of becoming an analytical chemist, to arm himself with a considerable share of patience, reminding him that it is not at one bound, but gradually, and step by step, that the student may hope to attain to that skill and precision in his operations that may justify reliance upon the correctness of his results. However mechanical, protracted, and tedious the operations of quantitative analysis may appear to be, the attainment of accuracy will amply compensate for the time and labor bestowed upon them ; whilst, on the other hand, nothing can be more disagreeable than to find, after a long and laborious process, that our results are incorrect or uncertain. Let him, therefore, who would render the study of quantitative analysis agreeable to himself, from the very outset endeavor, by strict, nay, scru- pulous adherence to the rules and conditions of this science, to attain to correct results, at any sacrifice of time. There cannot be a better and more immediate reward of labor than that which springs from the attainment of accurate results and perfectly corresponding analyses. The satisfaction enjoyed at the success of our efforts is surely in itself a sufficient motive for the necessary expenditure of time and labor, even without looking to the practical benefits which we may derive from our operations. The following are the substances treated of in this work : T. METALLOIDS, or NON-METALLIC ELEMENTS. Oxygen, Hydrogen, /Sulphur, [Selenium,] Phosjihorus, Chlorine, Iodine, Bromine, fluorine, Nitrogen, Boron, Silicon, Carbon. 6 INTRODUCTION. II. METALS. Potassium, Sodium, [Lithium,] Barium, Strontium, Calcium, Magne- sium, Aluminium, Chromium, [Titanium,] Zinc, Manganese, Nickel, Co- balt, Iron, [ Uranium,] Silver, Mercury, Lead, Copper, Bismuth, Cadmium, [Palladium,'] Gold, Platinum, Tin, Antimony, Arsenic, [Molybdenum]. The elements enclosed within brackets are considered in supplemen- tary paragraphs, and more briefly than the other elements. I have divided my subject into three parts. In the first, I treat of quantitative analysis generally ; describing, 1st, the methods of per- forming analytical operations and processes ; and, '2nd, the calculation of the results obtained. In the second, I give a detailed description of several special analytical processes. And in the third, a number of care- fully selected examples, which may serve as exercises for the groundwork of the study of quantitative analysis. The following table will afford the reader a clear and definite notion of the contents of the whole work : I. GENERAL PART. A DESCRIPTION OF THE ANALYTICAL METHODS AND PROCESSES. 1. Operations. 2. Reagents. 3. Forms and combinations in which substances are separated from others, or in which their weight is determined. 4. Determination of the weight of substances in simple compounds. 5. Separation of substances. 6. Organic elementary analysis. B CALCULATION OF THE RESULTS. II. SPECIAL PART. . 1. Analysis of natural springs, and more especially of mineral waters. 2. Analysis of such minerals and technical products as are most fre- quently brought under the notice of the chemist ; with comprehensive methods for ascertaining* their commercial value. 3. Analysis of the ashes of plants. 4. Analysis of soils. 5. Analysis of manures. 6. Analysis of atmospheric air. III. EXERCISES FOR PRACTICE. APPENDIX. 1. Analytical notes and experiments. 2. Tables for the calculation of analytical results. DIVISION I. GENERAL PART. SECTION I. ON THE METHODS OF PERFORMING ANALYTICAL PROCESSES. CHAPTER I. OPERATIONS. 1- MOST of the operations performed in quantitative research are the same as in qualitative analysis, and have been accordingly described in my work on that branch of analytical science. With respect to such operations I shall, therefore, confine myself here to pointing out any modifications they may require to adapt them for application in the quantitative branch ; but I shall, of course, give a full description of such as are resorted to exclusively in quantitative investigations. Opera- tions forming merely part of certain specific processes will be found described in the proper place, under the head of such processes. I. DETERMINATION OF THE QUANTITY. 2. The quantity of solids, and generally also that of fluids, is determined by weight ; the quantity of gases, and often also of fluids, by measure ; upon the care and accuracy with which these operations are performed, depends the value of all our results ; I shall therefore dwell minutely upon them. 3- 1. WEIGHING. To enable us to determine with precision the correct weight of a substance, it is indispensable that we should possess, 1st, a good BALANCE, and 2nd, perfectly accurate WEIGHTS. a. THE BALANCE. There are several points respecting the construction and properties of a good balance, which it is absolutely necessary for every chemist to understand. The usefulness of this indispensable instrument of quanti- tative chemistry depends upon two points ; 1st, its accuracy, and 2nd, its sensibility or delicacy. 8 "WEIGHING. [ 4-. 4. The ACCURACY of a balance depends upon the following conditions : a. The fulcrum must be placed above the centre of gravity of the beam. This is a condition essential to every balance. If the fulcrum were placed in the centre of gravity of the beam, the balance would not oscil- late, but remain in any position in which it is placed, assuming the scales to be equally loaded. If the fulcrum be placed below the centre of gravity of the beam, $he balance will be overset by the slightest impulse. When the fulcrum is above the centre of gravity of the beam the balance represents a pendulum, the length of which is equal to that of the line uniting the fulcrum with the centre of gravity, and this line forms right angles with the beam in whatever position the latter may be placed. Now if we impart an impetus to a ball suspended by a thread, the ball, after having terminated its vibrations, will invariably fall back into its original perpendicular position under the point of suspension. It is the same with a properly adjusted balance impart an impetus to it, and it will oscillate for some time, but it will invariably return to its original position ; in other words, its centre of gravity will finally fall back into its perpendicular position under the fulcrum, and the beam must consequently reassume the horizontal position. But to judge correctly of the force with which this is accomplished, and the velocity of the oscillations of a balance, it must be borne in mind that a balance is not a simple pendulum, but a compound one, i.e., a pendulum in which not one, but many material points move round the turning point, or pole. The inert mass to be moved is accordingly equal to the sum of these points, and the moving force is equal to the excess of the material points bflow over those above the fulcrum. ft. The suspension points of the scales must be on an exact level with the fulcrum. If the fulcrum be placed below the line adjoining the points of suspension, increased loading of the scales will continually tend to raise the centre of gravity of the whole system, so as to bring it nearer and nearer the fulcrum ; the weight which presses upon the scales com- bining in the relatively high-placed points of suspension ; at last, when the scales have been loaded to a certain degree, the centre of gravity will shift altogether to the fulcrum, and the balance will consequently cease to vibrate any further addition of weight will finally cause the beam to overset, by placing the centre of gravity above the fulcrum. If, on the other hand, the fulcrum be placed above the line joining the points of suspension, the centre of gravity will become more aud more depressed in proportion as the loading of the scales is increased ; the line of the pendulum will consequently be lengthened, and a greater force will be required to produce an equal turn ; in other words, the balance will grow the less sensible the greater the load. But when the three edges are placed on a level with each other, increased loading of the scales will, indeed, continually tend to raise the centre of gravity towards the fulcrum, but the former can in this case never entirely reach the latter, aud con- sequently the balance will never altogether cease to vibrate upon the further addition of weight, nor will its sensibility be lessened ; on the contrary, a greater degree of sensibility is imparted to it. This increase of sensibility is, however, compensated for by other circumstances. y. The beam must be sufficiently strong and inflexible to bear without bending the greatest weight that the construction of the balance ad/nits of; 5.] WEIGHING. 9 since the bending of the beam would of course depress the points of suspension so as to place them below the line of the fulcrum, and this would, as we have just seen, tend to diminish the sensibility of the balance in proportion to the increase of the load. It is, therefore, neces- sary to avoid this fault by a proper construction of the beam. The form best adapted for beams is that of a rhomb, or of an equicrural obtuse- angled triangle. 8. Tlie arms of the balance must be of equal length, i.e., the points of suspension must be equidistant from the fulcrum, or point of support ; for if the arms be unequal, the weights in equipoise will be unequal in the same proportion ; i.e. the weights in one scale, acting upon the longer arm of the lever, will preponderate over the exact equivalent in the other scale, and this in direct proportion to the greater or lesser excess of length of one arm over the other. 5. The SENSIBILITY, or DELICACY of a balance depends principally upon the following conditions : a. The friction of the edges upon tJieir supports must be as slight as pos- sible. The greater or lesser friction of the edges upon their supports depends upon both the form and material of those parts of the balance. The edges must be made of good steel, the supporters may be made of the same material ; it is better, however, that the centre edge should rest upon a perfectly horizontal agate plane. To form a clear conception of how necessary it is that even the lateral edges should have as little friction as possible, we need simply reflect upon what would happen were we to fix the scales in immovable points by means of inflexible rods. Such a contrivance would at once altogether annihilate the sensibility of a balance, for if a weight were placed upon one scale, this certainly would sink ; but at the same time, being compelled to form constantly a right angle with the beam, it would incline inwards, whilst the other scale would turn outwards, and thus the weight would be made to act upon the shorter arm of the lever. The more considerable the friction becomes at the end edges of a balance, the more the latter approaches the state just now described, and consequently the more is its sensibility impaired. )3. TJie centre of gravity must be as near as possible to the fulcrum. The nearer the centre of gravity approaches the fulcrum, the shorter be- comes the pendulum. If we take two balls, the one suspended from a short, and the other from a long thi-ead, and impart the same impetus to both, the former will naturally, in the extent of its vibrations, swing at a far greater angle from its perpendicular position than the latter. The same must of com-se happen with a balance ; the same weight will cause the scale upon which it is placed to turn the more rapidly and com- pletely, the shorter the distance between the centre of gravity and the fulcrum. We have seen above, that in a balance where the three edges are on a level with each other, increased loading of the scales will con- tinually tend to raise the centre of gravity towards the fulcrum. A good balance will therefore become more delicate in proportion to the increase of weights placed upon its scales, but, on the other hand, its sensibility will be diminished in about the same proportion by the in- crement of the mass to be moved, and by the increased friction attendant upon the increase of load ; in other words, the delicacy of a good balance ]0 WEIGHING. [ 6. will remain the same whatever may be the load placed upon it, ranging from the minimum .to the maximum that its construction will enable it to bear. y. The beam must be as light as possible. The remarks which we have just now made will likewise show how far the weight of the beam may influence the sensibility of a balance. We have seen that it is necessary that a balance should increase in delicacy in proportion to the increase of load, since the increased friction tends to diminish its delicacy in the same proportion ; and further, we have seen that this increase in sensi- bility is owing to the increased weight continually tending to raise the centre of gravity towards the fulcrum. Now it is evident, that the more considerable the weight of the beam is, the less will an equal load placed upon both scales alter the centre of gravity of the whole system, the more slowly will the centre of gravity approach the fulcrum, the less will the increased friction be neutralized, and consequently the less sensibility will the balance possess. Another point to be taken into account here is, that the respective moving forces being equal, a lesser mass or weight is more readily moved than a larger one (compare 4, a). We will now proceed, first, to give the student a few general rules to guide him in the purchase of a balance intended for the purposes of quan- titative analysis ; and, secondly, to point out the best method of testing the accuracy and sensibility of a balance. 1. A balance able to bear 70 or 80 grammes in each scale, suffices for most purposes. 2. The balance must be enclosed in a glass-case to protect it from dust. This case ought to be sufficiently large, and, more especially, its sides should not approach too near the scales. It must be constructed in a manner to admit of its being closed with facility when the weights have been placed on the scales, and thus to allow the operation of weighing being effected without any disturbing influence from currents of air. Therefore, either the front part of the case should consist of three parts, viz., a fixed centre piece and two lateral parts, opening like doors ; or, if the front part happens to be made of one piece, and arranged as A sliding-door, the two sides of the case must be provided each with a door. 3. The balance must be provided with a proper contrivance to render it immovable whilst the weights are being placed upon the scales. This is most commonly effected by an arrangement which enables the operator to lift up the beam and thus to remove the fulcrum from its support, whilst the scales remain suspended; other contrivances fix the scales, and leave the fulcrum resting on its support.* * One of my balances (made by the late M. Hoss, ofGiessen) is so arranged, that whilst the beam is lifted up by one stop, the scales may be supported from beneath, and thus fixed, by another independent contrivance, which is worked and regulated from the side. The movable supports which constitutes one of the principal parts of this contrivance, are provided at the top with crossed silk bands, and move with such perfect steadiness, that the scales do not shake in the least upon the removal of the supports from beneath them (provided, of course, the operation be effected with some degree of delicacy and caution). This arrangement, besides facilitating the loading of the scales, affords this advantage that it enables the operator to put an immediate stop to all trembling or shaking of the scales, and also the convenience that, in cases where one and the same body, 7.] WEIGHING. 11 But whatever contrivance may be had recourse to, at all events it is highly advisable to have the case of the balance so arranged that the processes of lifting up the beam, fixing the scales, &c., can be conducted while the case remains closed, and consequently from without. 4. It is necessary that the balance should be provided with an index to mark its oscillations ; this index is more appropriately placed at the bottom than at the side of the balance. 5. The balance must be provided with a pendulum, or with a spirit level, to enable the operator to place the three edges on an exactly horizontal level ; it is best also for this purpose that the case should rest upon three screws. 6. It is very desirable that the beam should be graduated into decimals, so as to enable the operator to weigh the milligramme and its fractions, by suspending a centigramme rider, or hook, on or between the indicated points of a graduated line, instead of placing the weight on the scale. Most modern balances are so constructed that the position of the riders on the beam may be shifted at pleasure, and without opening the glass case, by means of a movable arm placed in the side of the case. 7. The balance must be provided with a screw to regulate the centre of gravity, and likewise with two screws to regulate the equality of the arms, and finally with screws to restore instantly the equilibrium of the scales, should this have been disturbed. 7. The following experiments serve to test the accuracy and sensibility of a balance. 1. The balance is, in the first place, accurately adjusted, if necessary, either by the regulating screws, or by means of tinfoil, and a milli- gramme weight is then placed in one of the scales. A good and prac- tically useful balance must turn distinctly with this weight ; a delicate chemical balance should indicate the T ^ of a milligramme with perfect distinctness. 2. Both scales are loaded with the maximum weight the construction of the balance will admit of the balance is then accurately adjusted, and a milligramme added to the weight in the one scale. This ought to cause the balance to turn to the same extent as in 1. In most balances, however, it shows somewhat less on the index. 3. The balance is accurately adjusted, (should it be necessary to establish a perfect equilibrium between the scales by loading the one with a minute portion of tinfoil, this tinfoil must be left remaining upon the scale during the experiment) ; both scales are then equally loaded, say with about fifty grammes each, and, if necessary, the balance is again adjusted (by the addition of small weights, into the chamber, serves as pestle. The mortar is placed upon a solid support, and perpendicular blows are repeatedly struck upon the pestle until the object in view is attained. Minerals which are very difficult to pulverize should be ignited, and, when red hot, suddenly plunged into cold water, and subsequently again ignited, if necessary. This pi-ocess is of course applicable only to minerals which lose no essential constituent at a red heat, and are perfectly insoluble in water. In the purchase of agate mortars, especial care ought to be taken that they have no palpable fissures or inden- tations; very slight fissures, however, Fig. 21. do not render the mortar useless, al- though they impair its durability. Minerals insoluble in acids, and which consequently require fluxing, must be divided as finely as possible, otherwise we cannot calculate upon complete decomposition. This object may be obtained either by tritu- rating the pounded mineral with water, or by elutriation, or by sifting ; the two former processes, however, can be resorted to only in the case ol substances which are not attacked by water. It is quite clear that analysts must in future be much more cautious in this point than has hitherto been the case, since we know now that many substances which are usually held to be ftisoluble in water are, when in a state of minute division, strongly affected by that solvent ; thus, for instance, water, acting upon finely pulverized glass, is found to rapidly dissolve from 2 to 3 per cent, of the powder even in the cold. (Pelouze, " Compt. Rend." t. xliii., pp. 117-123.) Trituration with water (levigation). Add a little water to the pounded mineral in the mortar, and triturate the paste until all crepi- tation ceases, or, which is a more expeditious process, transfer the mineral paste from the mortar to an agate, flint, or porphyry slab, and triturate it thereon with a muller until it is perfectly smooth. Rinse the paste off, with the washing bottle, into a smooth porcelain basin of hemispheric form, evaporate the water on the water- bath, and mix the residue most carefully with the pestle. (The paste may be dried also in the agate mortar, but at a very gentle heat, since otherwise the mortar might crack.) To perform the process of elutriation, the pasty mass, having first been very finely triturated with water, is washed off into a beaker, and stirred with distilled water ; the mixture is then allowed to stand a minute or so, after which the supernatant turbid fluid is poured off into another beaker. The sediment, which contains the coarser parts, is then again subjected to the process of trituration and elutriation, &c., 26.] DESICCATION. 37 and the same operation repeated until the end in view is attained. The turbid fluid collected from the successive decantations is allowed to stand at rest until the minute particles of the substance held in sus- pension have subsided, which generally takes many hours. The clear supernatant fluid is then finally decanted, and the powder dried in the beaker. The process of sifting, or dusting, is conducted as follows : a piece of fine, well-washed, and thoroughly dry linen is placed over the mouth of a powder glass, about 10 centimetres high, and pressed down a little into the mouth, so as to form a kind of bag ; a portion of the finely triturated substance is put into the bag, and a piece of soft leather stretched tightly over the orifice, by way of cover. By drumming with the finger on the leather cover, a shaking motion is imparted to the bag, which makes the finer particles of the powder gradually pass through the linen. The portion remaining in the bag is subjected again to tritu- ration in an agate mortar, and, together with a fresh portion of the powdej, sifted again ; and the same process is continued until the entire mass has passed through the bag into the glass, in form of a most in- timately mixed, dusty powder. When operating on compound and mixed minerals, it would be a grave error indeed to use for analysis the powder resulting from the first pro- cess of elutriation or sifting, since this will contain the more readily pulverizable parts in a greater proportion to the more resisting parts, than is the case with the original substance. Great care must, therefore, also be taken to avoid a loss of substance in the processes of elutriation and sifting, as this loss is likely to be dis- tributed unequally among the several component parts. In cases where it is intended to ascertain the average composition of a mixed substance, of an iron ore for instance, a large average sample is selected, and reduced to a coarse powder ; the latter is thoroughly inter- mixed, and a portion of it then brought to the requisite degree of fineness. The most convenient and best-adapted instrument for the crushing and coarse pounding of large samples of ore, is a steel anvil and hammer. The anvil in my own laboi'atory consists of a wood pillar, 85 centimetres high and 26 centimetres in diameter, into which a steel plate, 3 centimetres thick and 20 centimetres in diameter, is let to the depth of one-half of its thickness. A brass ring, 5 centimetres high, is put round the upper projecting part of the steel plate. The hammer, which is well steeled, has a striking surface of 5 centimetres diameter. An anvil and hammer of this kind afford, among others, this advantage, that their steel surfaces admit most readily of cleaning> 26. 3. DESICCATION, OR DRYING. Substances which it is intended to analyse must be submitted to the requisite operations and processes in a clearly and distinctly characterized and definite state or form. In our introductory remarks we have laid it down as an indispensable condition of quantitative analysis, that the kind and nature of the con- stituents of the compounds under examination must be exactly and accu- rately known before we can proceed to their quantitative estimation. Now, the essential constituents of a substance are usually accompanied, by an accidental admixture, viz., a greater or less amount of water, in- 38 DESICCATION. [ 27. closed either within its lamellae, or adhering to it from the mode of its preparation, or absorbed by it from the atmosphere. It is perfectly obvious that to estimate correctly the quantity of a substance, we must, in the first place, remove the water which it may happen to hold in admixture. Most solid bodies, therefore, require to be dried before they can be quantitatively analysed. The operation of drying is of the very highest importance for the correctness of the results ; indeed it may safely be averred that many of the differences observed in analytical researches proceed entirely from the fact that substances are analysed in different states of moisture. It must be borne in mind, of course, that many substances contain water among their essential constituents (constitutional, or basic, water, and water of crystallization). With this water we must not interfere ; the operation of drying, which we have here in view, is intended only to remove the water accidentally admixed, or mechanically adhering to the substance, and which we will term here "moisture," the better to distinguish it from the water essentially inherent in a substanca Ac- cordingly, in the drying of substances for quantitative analysis, our only object is to remove all moisture from them, without interfering, in the slightest degree, with their constitutional water, or any other essential constituent. To accomplish this object, it is absolutely requisite that we should know the properties which the substance under examination manifests in the dry state, and whether it loses water or other consti- tuents at a red heat, or at 212 F., or in dried air, or even simply in contact with the atmosphere. These data will serve to guide us in the selection of the process of desiccation best suited to the substance under examination.* The following classification may accordingly be adopted : a. Substances which yield water even in simple contact with the at- inosphere ; such as sulphate of soda, crystallized carbonate of soda, &c. Substances of this kind turn dull arid opaque when exposed to the air, and finally crumble wholly or partially to a white powder. They are more difficult to dry than many other bodies. The process best adapted for the purpose, is to press the pulverized salts with some degree of force between thick layers of fine blotting-paper, until the last sheets remain It is generally advisable to subject the pulverized salts, in the course of this operation, once more to the process of trituration. b. Substances which do not yield water to the atmosjihere (unless perfectly dry), but effloresce in artificially dried air ; such as sulphate of magnesia, tartrate of potassa and soda (Rochelle salt), ut somewhat higher than b, or, as soon as the surface of the water ceases to close b, the re- mainder will flow out in a continuous stream. The process of washing by means of either of these bottles is easily performed. The bottle is placed inverted into the aperture contrived for its reception in the second arm of the filter-stand (see Fig. 47, 6), and 43.] SEPARATION OF PRECIPITATES. ?1 kept suspended above the funnel in such a manner that c just dips under the surface of the fluid. If the apparatus is well arranged, the water will now flow out of c in the same quantity as it runs off through the funnel. To use, instead of these washing-bottles, narrow-necked flasks, inverted directly into the funnel, is quite inadmissible in cases where it is in- tended to determine the exact amount of the precipitated substance ; since the ascending bubbles of air would invariably carry minute particles of the precipitate up into the flask. Care should be taken, whilst washing the precipitate, no matter whether with or without a washing apparatus, to prevent the formation of channels in it, through which the water might flow without per- vading the whole mass of the substance. If such channels have formed, the precipitate must be carefully stirred with a glass rod or a platinum spatula. As the use of washing-bottles tends to favor the formation of channels in precipitates in course of washing, it has of late been less employed, in the case of precipitates difficult to wash, the process described in 48 being resorted to in preference. The operation of washing may be considered completed when all soluble matter has been removed ; whether this has been effected, may generally be ascertained by evaporating a drop of the last washings upon a platinum knife, and observing whether or not this leaves a residue. But in cases where the precipitate is not altogether insoluble in water (sulphate of strontia, for instance), recourse must be had to more special tests, which we shall have occasion to point out in the course of the work. The operation of washing precipitates requires the greatest care and attention at the hands of the analytical chemist ; it is self-evident that the imperfect washing of a precipitate must materially interfere with the accuracy of the results. The operation should, therefore, never be deemed concluded on a mere impression to that effect which the operator may be led to entertain ; the information elicited by the application of the appropriate test or tests alone can safely be relied on. 48. SEPARATION OF PRECIPITATES BY DECANTATION AND FILTRATION COMBINED. In the case of precipitates which, from their gelatinous nature, or from an admixture of certain salts that have been thrown down along with them, appear to oppose insuperable or, at all events, considerable obstacles to perfect washing on the filter, the following method is resorted to. Let the precipitate subside as far as practicable, pour the nearly clear supernatant liquid on the filter, stir the precipitate up with the washing fluid (in certain cases, where such a course is indicated, the mixture of the washing fluid with the precipitate may 'besides be heated to boiling), let it subside again, and re] eat this operation until the pre- cipitate is almost thoroughly washed. Transfer it now to the filter, and complete the operation with the washing-bottle (see 47). This method ought to be resorted to more frequently than is usually the case ; there are many precipitates that can be thoroughly washed only by its appli- cation. In cases where it is not intended to weigh the precipitate washed by decantation, but to dissolve it again, the operation of washing is entirely 72 DRYING PRECIPITATES. [ 49, 50. completed by decantation, and the precipitate not even transferred to the filter. In such cases, the re-solution of the precipitate is effected in the vessel containing it, the filter being placed over the latter, and the solvent passed through it. Although the usual method applied to ascertain whether the operation of washing is actually completed, viz., testing a sample of the washings for one of the substances originally present in the solution from which the washed precipitate has been thrown down (for hydrochloric acid, for instance, with solution of nitrate of silver), will generally answer the purpose, there are cases in which it is not applicable. In such cases, and indeed in processes of washing by decantation generally, Bunserfs method is found the most convenient and practical ; viz., to continue the process of washing until the fluid which had remained in the beaker, after the first decantation, has undergone a ten thousand-fold dilution. To effect this, measure with a slip of paper, applied, of course, outside the vessel, the height from the bottom of this beaker to the surface of the fluid remaining in it, together with the precipitate, after the first decantation ; then fill the beaker with water, if possible, boiling, and measure the entire height of the fluid ; divide the length of the second column by that of the first. Go through the same process each time you add fresh water, and always multiply the quotient found with the number obtained in the preceding calculation, until you reach 10,000. 49. FURTHER TREATMENT OF PRECIPITATES PREPARATORY TO THE PROCESS OF WEIGHING. Before proceeding to weigh a precipitate, it is indispensable first to convert it into a form of accurately known composition. This is done either by drying the precipitate, or by heating it to redness. The former proceeding is more protracted and tedious in its application than the latter, and is, moreover, apt to give less accurate resulta The process of drying is, therefore, as a general rule, applied only to precipitates which cannot bear exposure to a red heat without undergoing total or partial volatilization ; or resorted to in cases where the residues left upon ignition have no uniform and constant composition ; thus, for instance, drying is resorted to in the case of sulphide of mercury, sulphide of lead, and other metallic sulphides ; and also in the case of cyanide of silver, potassio-bichloride of platinum, nium occasions no turbidity in the filtrate, although it may produce subsequently and a'"ter long standing suine slight and almost imponderable flakes of s.ilphide of zinc. 78.] PROTOXIDE OP MANGANESE. 113 tallized oxide of zinc is obtained (St. Claire Deville). Oxide of zinc is insoluble in water. Placed on moist turmeric paper, it does not change the color to brown. In acids, oxide of zinc dissolves readily, and with- out evolution of gas. When oxide of zinc is heated to redness with chloride of ammonium, fused chloride of zinc is produced, which volatilizes with very great difficulty, if the air is excluded ; but readily and com- pletely, with free access of air, and with chloride of ammonium fumes (H. Rose). COMPOSITION. Zn = 406-59 = 32-53 = 80-26 =100-00= 8-00= 19-74 506-59 = 4053 = 100-00 c. Sulphide of zinc, recently precipitated, is a white, loose mass (Zn S, H O), insoluble in water, in caustic alkalies, alkaline carbonates, and alkaline sulphides. It dissolves readily and completely in hydro- chloric acid and in nitric acid, but only very sparingly in acetic acid. When dried, the precipitated sulphide of zinc is a white powder ; at 212 F. it loses half, and at a red heat the whole of its water. During the latter process some sulphuretted hydrogen escapes, and the remain- ing sulphide of zinc contains an admixture of oxide of zinc. By roast- ing in the air, and intense ignition of the residue, small quantities of sulphide of zinc may be readily converted into the oxide. 78. 2. PROTOXIDE OF MANGANESE. Manganese is weighed either as PROTOSESQUIOXIDE OF MANGANESE (red oxide of manganese) Mn + Mn 2 3 ) = Mn 3 O 4 or as SULPHATE OF PROTOXIDE OF MANGANESE. For the purpose of converting it into the first form, it is precipitated as CARBONATE OF PROTOXIDE OF MANGANESE, HYDRATED PROTOXIDE OF MANGANESE, BINOXIDE OF MANGANESE, or SUL- PHIDE OF MANGANESE. a. Carbonate of protoxide of manganese, recently precipitated, is a white, flocculent mass, nearly insoluble in pure water, but somewhat more soluble in water impregnated with carbonic acid. Presence of carbonate of soda or potassa does not increase its solubility. Recently precipitated carbonate of protoxide of manganese dissolves pretty readily in solution of chloride of ammonium ; it is owing to this pro- perty that a solution of protoxide of manganese cannot be completely precipitated by carbonate of potassa or soda, in presence of chloride of ammonium (or some other ammoniacal salt), until the latter is com- pletely decomposed. If the precipitate, while still moist, is exposed to the air, or washed with water impregnated with air, it slowly assumes a dirty browtish- white color, part of it becoming converted into hydrated protosesquioxide of manganese. If the precipitate is dried removed from the contact of air, it forms a delicate white powder, persistent in the air [2 (Mn O, C O a ) + aq.] ; but when dried with free access of air, the powder is of a more or less dirty white color. When heated to redness, with access of air, this powder first turns black, and changes subsequently to brown protosesquioxide of manganese. However, this conversion takes some time, aud must never be held to be completed ii. I 114 PROTOXIDE OF MANGANESE. [ 78. until two weighings, between which the precipitate has been ignited again with free access of air, give perfectly corresponding results. b. Hydrated protoxide of manganese, recently thrown down, forms a white, flocculent precipitate, insoluble in water and in the alkalies, but soluble in chloride of ammonium ; this precipitate immediately absorbs oxygen from the air, and turns brown, owing to the formation of hy- drated protosesquioxide of manganese. On drying it in the air, a brown powder (hydrated protosesquioxide of manganese) is obtained which, when heated to intense redness, with free access of air, is converted into protosesquioxide of manganese. c. Protosesquioxide of manganese* (red oxide of manganese), artificially produced, is a reddish-brown powder. When exposed to the action of heat, it assumes a black tint, but its weight remains unaltered. It is insoluble in water, and does not alter vegetable colors. Heated to redness with chloride of ammonium, it is converted into protochloride of manga- nese (Mn g 4 + 4 H Cl = 3 Mn Cl + 01 + 4 H 0). COMPOSITION. 3 Mn = 1034-05= 8271= 72-10 4 O = 400-00= 32-00= 2790 1434-05 = 114-7 1 = 100-00 d. Binoxide of manganese is often produced in analysis by exposing a concentrated solution of nitrate of protoxide of manganese to a gradually increased temperature. At 284 F., brown flakes separate, at 311 F. much nitrous acid is disengaged, and the manganese sepai-ates asanhydrous binoxide. It is brownish black, and is deposited on the sides of the vessel, with metallic lustre. It is insoluble in weak nitric acid, but dissolves to a small amount in hot and concentrated nitric acid (Deville). In hydrochloric acid it dissolves with evolution of chlorine, in concentrated sulphuric* acid with evolution of oxygen. e. Sulphide of manganese, prepared in the humid way, forms a flesh- colored precipitate. From dilute neutral solution, and when precipitated by a limited quantity of sulphide of ammonium, it separates very slowly ; much more readily in presence of chloride of ammonium, or of an excess of sulphide of ammonium. Excess of ammonia must be guarded against in the process of precipitation ; otherwise some manganese is likely to remain in solution : the precipitation must be effected with yellow sulphide of ammonium, and not with the colorless compound, as the latter would dissolve traces of the precipitate. Presence of chloride of ammonium does not increase its solubility. In dilute acids (hydrochloric acid, sulphuric acid, acetic acid, s Carbonate of Baryta. a. In Solutions. Mix the moderately dilute solution of the baryta salt, in a beaker with ammonia, add carbonate of ammonia in moderate excess, and let the mixture stand several hours in a warm place. Filter, wash the precipitate with water mixed with a little ammonia, dry, and ignite ( 53). For the properties of the precipitate, see 71. This method involves a trifling loss of substance, as the carbonate of baryta is not absolutely insoluble in water. The direct experiment, No. 57, gave 99 '79 instead of 100 parts of baryta. If the solution contains a notable quantity of ammoniacal salts, the loss incurred is much more considerable, since the presence of such salts greatly increases the solubility of the carbonate of baryta. b. In Salts of Baryta with Organic Acids. Heat the salt slowly in a covered platinum crucible, until no more fumes are evolved ; place the crucible obliquely, with the lid leaning against it, and heat to redness, until the whole of the carbon is con- sumed, and the residue presents a perfectly white appearance ; moisten the residue with a concentrated solution of carbonate of ammonia, evaporate, ignite gently, and weigh. The results obtained by this method are quite satisfactory. A direct experiment, No. 58, gave 99-61 instead of 100 parts of baryta. The loss of substance, which almost invariably attends this method, is owing to particles of the salt being carried away with the fumes evolved upon ignition, and is accordingly the less considerable, the more slowly and gradually the heat is increased. Omission of the moistening the residue with carbonate of ammonia would involve a further loss of substance, as the ignition of carbonate of baryta in contact with carbon is attended with formation of some caustic baryta, and evolution of carbonic oxide gas. 102. 2. STRONTIA. a. Solution. Seethe preceding paragraph ( 101, a. Solution of baryta), the direc- tions there given applying equally here. b. Determination. Strontia is weighed either as sulphate or as carbonate ofstrontia( 7'2). Strontia in the pure state, or in form of carbonate, may be determined also by the volumetrical (alkalimetrical) method.Oo nip. 223. * I mention this in reference to Sieyle's statement in the " Journal f. prakt. Cliem.," 69, 142, that acetic acid and nitric acid will still extract small quantities of chloride of barium from sulphate of baryta, farmed in presence of au excess of sulphuric acid, aiid thoroughly washed with water. 102.] STROXTIA. 155 We may convert into 1. SULPHATE OF STROXTIA. a. By Precipitation. All compounds of strontia without exception. 6. By Evapijration. All salts of strontia with volatile acids, if no other non-volatile body is present. 2. CARBONATE OF STRONTIA. a. All compounds of strontia soluble in water. . Salts of strontia with organic acids. The method based on the precipitation of strontia with sulphuric acid yields accurate results only in cases where the fluid from which the strontia is to be precipitated may be mixed, without injury, with alcohol. Where this cannot be done, and where the method based on the evaporation of the solution of strontia with sulphuric acid is equally inapplicable, the conversion into the carbonate ought to be resorted to in preference, if admissible, in the case of soluble compounds of strontia and of salts of strontia with organic acids. 1. Determination as Sidpliate of Strontia. a. By Precipitation. Mix the solution of the salt of strontia (which must not be too dilute, nor contain much free hydrochloric or nitric acid), with dilute sul- phuric acid in excess, in a beaker, and add, at least, an equal volume of alcohol ; let the mixture stand a few hours, and filter ; wash the precipitate with dilute spirit of wine, dry, ignite, and weigh the residue ( 53). If the circumstances of the case contraindicate the use of alcohol, the fluid must be precipitated in a tolerably concentrated state, allowed to stand in the cold for at least twenty-four hours, filtered, and the pre- cipitate washed with cold water, until the last rinsings manifest no longer au acid reaction, and leave no perceptible residue upon evaporation. If traces of free sulphuric acid remain adhering to the filter, the latter turns black on drying, and crumbles to pieces ; too long protracted washing of the precipitate, on the other hand, tends to increase the loss of substance inseparable from the application of this method in cases where the use of alcohol is inadmissible. Care must be taken that the precipitate be thoroughly tiry, before proceeding to ignite it ; otherwise it will be apt to throw oft' fine particles during the latter process. The filter, which is to be burnt on the lid of the crucible, must be as clean as possible, or some loss of sub- stance will be incurred ; as may be clearly seen from the depth of the carmine tint of the flame with which the filter burns if the precipitate has not been properly removed. For the properties of the precipitate, ^ee 72. This method gives very accurate results in cases where the addition of alcohol to the solu- tion is admissible ; but where we have to deal with a simple aqueous solution, a rather considerable loss is unavoidable, as sulphate of strontia is uot absolutely insoluble in water. The direct experiments, No. 59, gave only 98*12 and 98 02 instead of 100 parts of stroutia. However, the error may, in a great measure, be rectified, by calculating the amount of sulphate of strontia dissolved in the filtrate and the rinsing water, basing the calculation upon the known degree of solubility of sul- 156 LIME. [ 103. phate of strontia in pure and acidified water. See Experiment No. 60, which, with this correction, gave 9977 instead of 100 parts of strontia. b. By Evaporation. The same method as described 101, 1, 6. 2. Determination as Carbonate of Strontia. a. In Solutions. The same method as described 101, 2, a. For the properties of the precipitate, see 72. The method gives very accurate results, as car- bonate of strontia is nearly absolutely insoluble in water containing am- monia and carbonate of ammonia. A direct experiment, No. 60, gave 99-82 instead of 100 parts of strontia. Presence of ammouiacal salts exercises here a less adverse influence, than in the precipitation of car- bonate of baryta. b. In Salts with Organic Matter. The same method as described 101, 2, b. The remarks made there, respecting the accuracy of the results, apply equally here. 103. 3. LIME. a. Solution. See 101 a. Solution of baryta. Fluoride of calcium is, by means of sulphuric acid, converted into sulphate of lime, and the latter again, if necessary, decomposed bv boiling or fluxing with an alkaline cai - - bonate ( 132). b. Determination. Lime is weighed either as sulphate, or as carbonate of lime ( 73). Small quantities of lime are also occasionally reduced to the caustic state, instead of being converted into carbonate. Lime in the pure state, or in form of carbonate, may be determined also by the volunietrical (alkalimetrical) method. Comp. 223. We may convert into 1. SULPHATE OF LIME. a. By Precipitation. All salts of lime with acids soluble in alcohol, provided no other sub- stance insoluble in alcohol be present. b. By Evaporation. All salts of lime with volatile acids, provided no non-volatile body be present. 2. CARBONATE OF LIME. a. By Precipitation tinth Carbonate of Ammonia. All salts of lime soluble in water. b. By Precipitation with Oxalate of Ammonia. All salts of lime soluble in water or in hydrochloric acid. c. By Ignition. Salts of lime with organic acids. Of these several methods, 2, b. (precipitation with oxalate of ammonia) is the one most frequently resorted to. This, aud the method 1, b, give the most accurate results. The method, 1, a, is usually resorted to only 103.] LIMP, 157 to effect the separation of lime from other bases ; 2, a, generally only to effect the separation of lime together with other alkaline earths from the alkalies. 1. Determination as Sulphate of Lime, a. By Precipitation. Mix the solution of lime in a beaker, with dilute sulphuric acid in excess, and add twice the volume of alcohol : let the mixture stand twelve hours, niter, and tliorougldy wash the precipitate with spirit of wine, dry, and ignite moderately ( 53). For the properties of the pre- cipitate, see 73. The results are very accurate. A direct experi- ment, No. 62, gave 99-64 instead of 100 parts of lime. b. By Evaporation. The same method as described 101, 1, b. See also 103, 2, &, a. 2. Determination as Carbonate of Lime. a. By Precipitation with Carbonate of A mmonia. The same method as described 101, 2, a. The precipitate must be exposed only to a very gentle red heat, but this must be continued for some time. For the properties of the precipitate, see 73. This method gives very accurate results, the loss of substance incurred being hardly worth mentioning. If the solution contains chloride of ammonium or similar ammoniacal salts in considerable proportion, the loss of substance incurred is far greater. The same is the case if the precipitate is washed with pure instead of ammoniacal water. A direct experiment, No. 63, in which pure water was used, gave 99 '17 instead of 100 parts of lime. b. By Precipitation with Oxalate of Ammonia, a. TJie Lime Salt is soluble in Water. Dissolve the salt in hot water, in a beaker; add oxalate of ammonia in moderate excess, and then ammonia sufficient to impart an anuiio- niacal smell to the fluid ; cover the glass, and let it stand in a warm place until the precipitate has completely subsided, which will require twelve hours, at least. Pour the clear fluid gently and cautiously, so as to leave the precipitate undisturbed, on a proper filter. As soon as the fluid has passed through, transfer the precipitate also to the filter, by rinsing with hot water, taking care, after the addition of every fresh portion, to wait until the fluid has completely passed through the filter. Small particles of the precipitate, adhering more firmly to the glass, are removed with a feather. If this fails to effect their complete removal, tht>y should be dissolved, in a small vessel, in a few drops of highly dilute hydro- chloric acid, ammonia added to the solution, and the oxalate obtained added to the first precipitate. Deviations from the rules laid down here will generally give rise to the passing of a turbid fluid through the filter. After having washed the precipitate, dry it on the filter in the funnel, and transfer the dry precipitate to a platinum crucible, taking care to scrape the filter as clean as practicable ; burn the filter on a piece of platinum wire, letting the ash drop into the hollow of the lid ; put the latter, now inverted, on the crucible, to prevent the filter ash mixing with the precipitate ; apply a gentle heat, and increase this gradually, until the bottom of the crucible is heated to very faint i-edness. Keep it at that temperature from ten to fifteen minutes, then let it cool, T58 HUE. [ 103. and weigh. After this, moisten the contents of the crucible, which must be perfectly white, or barely show the least tinge of gray, with a little water, and test this after a time with a slip of turmeric paper. If the color of the' test paper remains unaltered, the process may be considered at an end, and the result taken as correct ; but should the paper turn brown a sign that the heat applied was too intense rinse off the fluid adhering to the paper with a little water into a crucible, throw in a small lump of pure carbonate of ammonia, evapo- rate to dryness (best in the water-bath), heat to very faint redness, and weigh the residue. If the weight shows an increase over that of the first residue, repeat the same operation until the weight remains constant. This method, if properly and carefully performed, in strict accordance with the directions, gives nearly absolutely accurate results ; and if the application of heat is properly managed, there is no need of the tedious supplementary operation recommended here evaporation with carbonate of ammonia. A direct experiment, No. 67, gave 99'90 instead of 100 parts of lime. For the properties of the precipitate and residue, see 73. If the quantity of oxalate of lime obtained is only very trifling, I prefer to convert it into the sulphate, or to reduce it to the caustic state. To effect the latter, the oxalate of lime is heated to intense red- ness, in a small platinum crucible, over a gas blowpipe-flame, and the operation continued long enough to effect the reduction of the oxalate to the caustic state. The conversion of the oxalate into sulphate is effected most conveniently by Schrotters method, viz., ignition with pure sulphate of ammonia. Many chemists prefer collecting the oxalate of lime upon a weighed filter, drying at 212 F., and weighing the dry precipitate. This pre- cipitate is not, as is often erroneously supposed, Ca O, C S O 3 , but, Ca O, C 4 O S 4- aq., and must therefore be calculated as such. This method, besides being more tedious, gives less accurate results than that based on the conversion of the oxalate into the carbonate. The direct experiment, No. 65, gave 100-45 instead of 100 parts of lime. Instead of weighing the oxalate of lime as such, or in form of car- bonate, &c., the quantity of lime present in the salt may be determined also by two different volumetrical methods. a. Ignite the oxalate, converting it thus into a mixture of carbo- nate and caustic lime, and determine the quantity of the lime by the alkalimetrical method described in 223 ; or, b. Determine the oxalic acid in the well-washed but not yet dried oxalate of lime, by means of permanganate of potassa ( 137), and reckon for each equivalent of oxalic acid (C a O 3 ) an equivalent of lime (He/njiel). With proper care, both these volumetrical methods give as accurate results as those obtained by weighing. (Comp. Experiment No. 66.) They deserve to be recommended more particularly in cases where an entire series of quantitative estimations of lime has to be made. Under cer- tain circumstances it may also prove advantageous to precipitate the lime with a measured quantity of a standard solution of oxalic acid or quadraoxalate of potassa, filter, and determine the excess of oxalic acid in the filtrate (Kraut. " Chem. Centralblatt," 1856, 316). j3. The Salt is insoluble in Water. Dissolve the salt in dilute hydrochloric acid. If the acid com- bined with the lime is of a nature to escape in this operation (e. g., 10k] , MAGNESIA. 159 carbonic acid), or to admit of its separation by evaporation (e. g., silicic acid), proceed, after the removal of the acid, as directed in a. But if the acid is of more stable nature (e. g., phosphoric acid), neu- tralize the free acid present with ammonia until a precipitate begins to form, re-dissolve this again with a drop of hydrochloric acid, add oxalate of ammonia in excess, and finally acetate of soda ; allow the pre- cipitate to subside, and proceed for the remainder of the operation as directed in a. In this process the free hydrochloric acid present com- bines with the ammonia and soda of the oxalate and acetate, liberating a corresponding quantity of oxalic acid and acetic acid, in which acids oxalate of lime is nearly insoluble. The method yields pretty accurate results. A direct experiment, No. 67, gave 99 '78 instead of 100 parts of lime. c. By Ignition. The same method as described 101, 2, b (baryta). The residue re- maining upon evaporation with carbonate of ammonia (which operation it is advisable to perform twice) must be ignited very gently. The re- marks made in 101, 2, 6, in reference to the accuracy of the results, apply equally here. By way of control, the carbonate of lime may be converted into sulphate or reduced to the caustic state. See b, a. 104. 4. MAGNESIA. a. Solution. Many of the compounds of magnesia are soluble in water ; those which are insoluble in that menstruum dissolve in hydrochloric acid, with the exception of some silicates and aluminates. b. Determination. Magnesia is weighed either as sulphate of magnesia, or as pyrophos- phate, or as pure magnesia. In the pure state, or in form of carbonate, it may be determined also by the alkalimetrical method described in 223. We may convert into 1. SULPHATE OF MAGNESIA. a. Directly. b. Indirectly. All compounds of magnesia with All compounds of magnesia so- volatile acids, provided no other luble in water, and also those non volatile substance be present. which, insoluble in that menstruum, dissolve in hydrochloric acid, with separation of their acid (provided no ammoniacal salts be present). 2. PYROPHOSPHATE OF MAGNESIA. All compounds of magnesia without exception 3. PURE MAGNESIA. a. Salts of magnesia with organic acids, or with readily volatile in- organic oxygen acids. b. Chloride of magnesium, and the compounds of magnesia convertible into that salt. The direct determination as sulphate of magnesia is highly recom- mended in all cases where it is applicable. The indirect conversion into the sulphate serves only to separate magnesia from certain bases, 160 PURE MAGNESIA. [ 104. and is hardly ever had recourse to where it can possibly be avoided. The method based on the conversion of the magnesia compound into the pyrophosphate is most generally resorted to; especially also to effect the separation of magnesia from other bases. The method based on the con- version of chloride of magnesium into pure magnesia is usually resorted to only to effect the separation of magnesia from the fixed alkalies. Compounds of magnesia with phosphoric acid are analysed as 134 directs. 1 . Determination as Sulphate of Magnesia. a. Direct Determination. Add to the solution of magnesia a more than sufficient amount of dilute pure sulphuric acid to combine with the whole of the magnesia present, evaporate the mixture to dryness, in a weighed platinum dish, on the water-bath ; heat cautiously at first, then, after putting on the lid, more strongly, until the excess of sulphuric acid is completely expelled ; heat the residue now over the lamp for some time to gentle redness ; let it cool, and weigh. Should no fumes of hydrated sulphuric acid escape upon the application of a stronger heat, this may be looked upon as a sure sign that the sulphuric acid has not been added in sufficient quan- tity, in which case the mixture is allowed to cool, and a fresh portion of sulphuric acid added. The method yields very accurate results. Care must be taken not to use a very large quantity of sulphuric acid, since this would tend to protract the process unnecessarily; the residue must be exposed to a moderate red heat only, and weighed as soon as cold. For the properties of the residue, see 74. b. Indirect Determination. The solution of magnesia is heated, in a flask, to 212 F., and clear saturated water of baryta added in excess; the temperature is maintained near the boiling point for some time; the fluid is then filtered off from the precipitate, and the latter carefully washed with boiling water, and subsequently dissolved upon the filter, with somewhat dilute warm hydrochloric acid ; the filter is also carefully washed, and the further operation conducted as directed in a. Should a precipitate of sulphate of baryta form upon the addition of the sulphuric acid, this may be con- sidered a sign that the carbonic acid of the air has not been sufficiently excluded from contact with the water of baryta during the operation. In that case, we may either allow this precipitate to subside, filter, and evaporate the filtrate ; or we may evaporate at once, weigh the residue, dissolve in water containing hydrochloric acid, filter the solution off from the undissolved sulphate of baryta, ascertain the weight of the latter ( 101, 1, a), and subtract this from the original residue. The results obtained by this method fall somewhat short of 100, since hydrated magnesia is not quite insoluble in water. The method is, more- over, rather too complicated to yield perfectly accurate results. 2. Determination as Pyroplwspliate of Magnesia. The solution of the salt of magnesia is mixed, in a beaker, with chloride of ammonium, and ammonia added in slight excess. Should a precipitate form upon the addition of ammonia, this may be considered a sign that a sufficient amount of chluricle of ammonium has not been used ; a fresh amount of that salt must consequently be added, sufficient to effect the re-solution of the precipitate formed. The fluid is then mixe.l 101.] MAGNESIA. 161 with a solution of phosphate of soda in excess, and the mixture stirred, with a glass rod, taking care to avoid touching the sides of the beaker with the stirring-rod ; otherwise particles of the precipitate are apt to adhere so firmly to the rubbed parts of the beaker, that it will be found difficult to remove them ; the beaker is then well covered, and allowed to stand at rest for twelve hours, in a moderately warm place ; after that time the fluid is filtered, and the precipitate collected on the filter, the last pai'ticles of it being rinsed out of the glass with a portion of the filtrate, with the aid of a feather ; when the fluid has com- pletely passed through, the precipitate is cai'efully washed with a mix- ture of 3 parts of water, and 1 part of solution of ammonia of 0'9fi specific gravity, the operation being continued until a drop of the fluid passing through the filter no longer leaves a residue when evaporated upon a platinum knife. The precipitate is now thoroughly dried, and then transferred to a platinum crucible ( 53); the latter, with the lid on, is exposed for some time to a very gentle heat, which is finally increased to intense redness. The filter, scraped as clean as practicable, is incinerated in a spiral coil of platinum wire, and the ash transferred to the crucible, which is then once more exposed to a red heat, allowed to cool, and weighed. For the properties of the precipitate and residue, see 74. This method, if properly executed, yields most accurate results. Direct experiments, No. 66 a and b, gave respectively 100*09 and 99 '97 instead of 100 parts of magnesia. 3. Determination as pure Magnesia. a. In Salts of Magnesia with Organic or Volatile Inorganic Adds. The salt of magnesia is gently heated in a covered platinum crucible, increasing the temperature gradually, until no more fumes escape ; the lid is then removed, and the crucible placed in an oblique position, with the lid leaning against it. A red heat is now applied, until the residue presents a perfectly white appearance. For the pro- perties of the residue, see 74. The method gives pretty accurate results, provided the application of heat be managed slowly and gradually. Some loss of substance is usually sustained, owing to traces of the salt being carried oft' with the empyreumatic products. Salts of magnesia with readily volatile oxygen acids (carbonic acid, nitric acid), may be reduced to magnesia in a similar way, by simple ignition. Even sulphate of magnesia is completely reduced to the caustic state when exposed, in a platinum crucible, to the heat of the gas blowpipe- flame (Sonnenschein). As regards small quantities of sulphate of mag- nesia, I can fully confirm this statement. b. Conversion of Chloride of Magnesium into pure Magnesia. The concentrated solution of chloride of magnesium is mixed in a porcelain crucible, with levigated pure oxide of mercury, added in pro- portion more than sufficient to convert by its oxygen the whole of the magnesium present into magnesia. The mixture is evaporated on the water-bath, and the residue thoroughly dried ; the crucible is now covered, and exposed to a red heat, until the chloride of mercury formed is expelled, together with the excess of oxide of mercury. The operator should carefully guard against inhaling the fumes evolved. The residue II. M 162 PURE ALUMINA. [ 105. of magnesia is either weighed at once in the crucible, or if the operation had for its object the separation of the earth from the alkalies, it is col- lected upon a filter, washed with hot water, dried, and ignited ( 53). Compare also 153, B, 4 (17-21), where some other methods are given to effect the same purpose. THIRD GROUP OF THE BASES. ALUMINA SESQUIOXIDE OF CHROMIUM (TITANIC ACID). 105. 1. ALUMINA. a. Solution. Those of the compounds of alumina which are insoluble in water, dis- solve, almost without exception, in hydrochloric acid. Native crystallized alumina (sapphire, ruby, corundum, &c.), and many native alumina com- pounds, and also artificially produced alumina, after intense ignition, re- quire fluxing with carbonate of soda, caustic potassa, or hydrate of baryta, as a preliminary step to their solution in hydrochloric acid. Many alumina compounds which resist the action of concentrated hydrochloric acid, may be decomposed by protracted treatment with concentrated sul- phuric acid, or by fusion with bisulphate of potassa ; e.g. common clay. b. Determination. Alumina is invariably weighed in the pure state ( 75). The several compounds of alumina are converted into pui-e alumina, either by preci- pitation as hydrate of alumina, and subsequent ignition, or by simple ignition. We may convert into PURE ALUMINA. a. By Precipitation. b. By Heating or Ignition. All compounds of alumina soluble a. All salts of alumina with in water, and those which, insoluble readily volatile acids (sesquichloride in that menstruum, dissolve in hy- of aluminium, nitrate of alumina, drochloric acid, with separation of &c.) their acid. ft. All salts of alumina with or- ganic acids. The methods b, a, and /3, are applicable only in cases where no other- fixed substances are present. The method of estimating alumina in its combination with phosphoric acid, boracic acid, silicic acid, and chromic acid, will be found in Part II. of this section, under the respective heads of these several acids. a. By Precipitation. Mix the moderately dilute hot solution of alumina, in a beaker, with a pretty considerable quantity of chloride of ammonium, if that salt is not already present ; add ammonia slightly in excess, and let the mix- ture stand for 12 hours in a warm place; then decant the clear super- natant fluid on to a filter, taking care not to disturb the precipitate ; pour boiling water on the latter in the beaker, stir, let the saline particles subside, decant again, and repeat this operation of washing by 106.] SESQUIOXIDE OF CHROMIUM. 163 decantation a second and a third time ; transfer the precipitate now to the filter, wash once more with boiling water, dry thoroughly, ignite ( 52), and weigh. The heat applied should be very gentle at first, and the crucible kept well covered, to guard against the risk of loss of substance from spurting, which is always to be apprehended if the pre- cipitate is not thoroughly dry ; towards the end of the process the heat should be raised to intense redness. In the case of sulphate of alumina the foregoing process is apt to leave some sulphuric acid iu the precipitate, which, of course, vitiates the result. To ensure the removal of this sulphuric acid, the precipitate should be exposed for a quarter of an hour to the heat of the gas blow-pipe flame. If there are difficulties in the way, preventing this proceeding, the precipitate, either simply washed or moderately ignited, must be re-dissolved in hydrochloric acid (which requires protracted warming with strong acid), and then pre- cipitate again with ammonia ; or the sulphate must first be converted into nitrate by decomposing it with nitrate of oxide of lead, added in very slight excess, the excess of lead removed by means of hydrosulphuric acid, and the further process conducted according to the directions of a, or b. For the properties of hydrate of alumina and ignited alumina, see 75. The method, if properly executed, gives very accurate results. But if a considerable excess of ammonia is used, more particularly when no ammoniacal salts are present, and when the addition of chloride of ammonium has been omitted, a very considerable loss is likely to be incurred ; this loss is the greater the more dilute the solution, and the shorter the time which elapses between the precipitation and de- cantation. b. By direct Ignition. a. Compounds of Alumina w th volatile Acids. aa. In tlie solid State. Expose the salt (in the case of sesquichloride of aluminium, after pre- vious addition of water), in a platinum crucible, to a red heat, gentle at first, but increased gradually to the very highest degree of intensity, until the weight remains constant. For the properties of the residue see 75. The purity of the residue must be carefully tested. This method gives accurate results. bb. In Solution. Evaporate the solution to dryness on the water-bath, and proceed with the residue as directed in aa. (3. Compounds of Alumina with Organic Acids. The same method as described 104, 3. a (Magnesia). 106. 2. SESQUIOXIDE OF CHROMIUM. a. Solution. Many of the compounds of sesquioxide of chromium are soluble in water. Hydrated sesquioxide of chromium, and most of the salts of ses- quioxide of chromium insoluble in water, dissolve in hydrochloric acid. Ignition renders sesquioxide of chromium and many of its salts insoluble in acids ; this insoluble modification must be prepared for solution in hydrochloric acid, by fluxing with 3 or 4 parts of carbonate of soda. A small quantity of sesquioxide of chromium is converted, in the process M2 164 PURE SESQUIOXIDE OF CHROMIUM. [ 106. of fluxing, into chromic acid, by the action of the air ; this is, however, reduced again to sesquioxide upon heating with hydrochloric acid. Addition of alcohol greatly promotes the reduction. For the solution of chrome -ironstone, see 160. b. Determination. Sesquioxide of chromium may be weighed in the pure state, or it may be converted into chromic acid, and its weight calculated from the amount of the latter (see 130). The several compounds of sesquioxide of chromium are reduced to the sesquioxide either by precipitation as hydrated sesquioxide, and subsequent ignition, or by simple ignition. We may convert into 1. PURE SESQUIOXIDE OF CHROMIUM. a. By Precipitation. b. By Ignition. All compounds of sesquioxide of a. All salts of sesquioxide of chromium soluble in water, and also chromium with volatile oxygen those which, insoluble in that men- acids, provided no non-volatile sub- struum, dissolve in hydrochloric stances be present, acid, with separation of their acid. ft. Salts of sesquioxide of chro- mium with organic acids. 2. CHROMIC ACID, or, more correctly speaking, ALKALINE CHROMATE. Sesquioxide of chromium and all its salts. The methods of estimating the sesquioxide of chromium in its combi- nations with chromic acid, phosphoric acid, boracic acid, and silicic acid, will be found in Part II. of this section, under the respective heads of these several acids. 1. Determination as Sesquioxide of Chromium. a. By Precipitation. The salt is dissolved in a beaker, and the solution, which must not be too highly concentrated, heated to212F. Ammonia is then added slightly in excess, and the mixture exposed to a temperature approaching boiling, until the fluid over the precipitate is perfectly colorless, presenting no longer the least shade of red ; let the solid par- ticles subside, wash three times by decantation, and lastly once more on the filter, with hot water, dry thoroughly, and ignite ( 52). The heat in the latter process must be increased gradually, and the crucible kept covered, otherwise some loss of substance is likely to arise from spurting upon the incandescence of the sesquioxide of chromium which marks the passing of the soluble into the insoluble modification. For the pro- perties of the precipitate and residue, see 76. This method, if properly executed, gives very accurate results. b. By direct Ignition. a. Salts of Sesquioxide of Chromium with Volatile Acids. The same method as described, 105, b, a (Alumina). b. Salts of Sesquioxide of Chromium with Organic Acids. The same method as described 104, 3, a (Magnesia). 2. CONVERSION OF SESQUIOXIDE OF CHROMIUM INTO CHROMIC ACID (in combination with an alkali). (For the estimation of chromic acid, see 1 30.) 107.] TITANIC ACID. 165 The following methods have been proposed to effect the conversion of sesquioxide of chromium into an alkaline chromate. a. The solution of the salt of sesquioxide of chromium is mixed with solution of potassa or soda in excess, until the hydrated sesquioxide, which forms at first, is redissolved. Chlorine gas is then conducted into the cold fluid until it acquires a yellowish-red tint ; it is then mixed with potassa. or soda in excess, and the mixture evaporated to dry ness ; the residue is ignited in a platinum crucible. The whole of the chlorate of potassa (or soda) formed is decomposed by this process, and the residue consists, therefore, now of an alkaline chromate and chloride of potassium (or sodium). ( Vohl.) b. Hydrate of potassa is heated in a silver crucible to calm fusion ; the heat is then somewhat moderated, and the perfectly dry compound of sesquioxide of chromium put in the crucible. When the sesquioxide of chromium is thoroughly moistened with the hydrated potassa, small lumps of fused chlorate of potassa are added. A lively effervescence ensues, from the escape of oxygen ; at the same time the mass acquires a more and more yellow color, and finally becomes clear and transparent. Loss of substance must be carefully guarded against {If. Schwarz). c. Dissolve the sesquioxide of chromium in solution of potassa or soda, add binoxide of lead in sufficient excess, and warm. The yellow fluid produced contains all the chromium as chromate of lead in the alkaline solution. Filter from the excess of binoxide of lead, add to the filtrate acetic acid to acid reaction, and determine the weight of the precipitated chromate of lead (G. Chancel. " Comp. rend.," 43, 927.) 107. Supplement to the Third Group. TITANIC ACID. Titanic acid is always weighed in the pure state ; its separation is effected either by precipitation with ammonia, or from dilute acid solu- tion, by boiling. In precipitating acid solutions of titanic acid with ammonia, take care to add the precipitating agent only in slight ex- cess, let the precipitate formed, which resembles hydrate of alumina, deposit, wash, first by decantation, then completely on the filter, dry, and ignite ( 52). If the solution contained sulphuric acid, put some carbonate of ammonia into the crucible, after the first ignition, to secure the removal of every remaining trace of that acid. Lose no time in weighing the ignited titanic acid, as this substance is slightly hygroscopic. From very dilute solutions of titanic acid in sulphuric acid, obtained by treating with cold water the mass produced by fusing titanic acid with bisulphate of potassa, the titanic acid may be separated also by protracted boiling, with renewal of the evaporating waters ; the pre- cipitate is washed simply with water. In the process of ignition some carbonate of ammonia is added to the dried precipitate. From dilute hydrochloric acid solutions of titanic acid, the latter separates completely only upon evaporating the fluid to dry ness ; and if the precipi- tate in that case were washed simply with water, it would pass through the filter in a milky condition ; acid must, therefore, be added to the water. Hydrate of titanic acid precipitated in the cold, washed with cold 166 OXIDE OF ZINC. [ 108. water, and dried without elevation of temperature, is completely soluble in hydrochloric acid ; produced by precipitation, under different circum- stances, it dissolves only incompletely in that acid. Titanic acid thrown, down from dilute acid solutions by boiling, is not soluble in dilute acids. Ignited titanic acid does not dissolve even in concentrated hydrochloric acid ; rather concentrated sulphuric acid will dissolve it, however, upon continued application of heat. The easiest way of effecting its solution is to fuse it for some time with bisulphate of potassa, and treat the fused mass with a large quantity of cold water. Upon fusing titanic acid with carbonate of soda, titanate of soda is formed, which, when treated with water, leaves acid titanate of soda, soluble in hydrochloric acid. Titanic acid (Ti O 2 ) consists of 6 1 '2 per cent, of titanium, and 38'8 per cent, of oxygen. FOURTH GROUP OF THE BASES. OXIDE OF ZINC PROTOXIDE OF MANGANESE PROTOXIDE OF NICKEL PROTOXIDE OF COBALT PROTOXIDE OF IRON SESQUIOXIDE OF IRON (SESQUIOXIDE OF URANIUM). 108. 1. OXIDE OF ZINC. a. Solution. Many of the salts of zinc are soluble in water. Metallic zinc, oxide of zinc, and the salts of zinc, which are insoluble in water, dissolve in hydrochloric acid. b. Determination. Oxide of zinc is invariably weighed as such ( 77). The conversion of the salts of zinc into the oxide is effected either by precipitation as carbonate or sulphide of zinc, or by direct ignition. Besides these gravi- metric methods, there have been proposed and adopted also several volumetric methods. We may convert into OXIDE OF ZINC. a. By Precipitation as Carbonate b. By Precipitation as Sulphide of Zinc. of Zinc. All the salts of zinc which are All compounds of zinc without soluble in water, and all those with exception, organic volatile acids ; also those salts of zinc which, insoluble in water, dissolve in hydrochloric acid, with separation of their acid. c. By direct Ignition. Salts of zinc with volatile inorganic oxygen acids. The last method is to be recommended only for carbonate of zinc and nitrate of zinc. Sulphide of zinc and sulphate of zinc require a white heat for their complete conversion into the oxide (the former with access of air). The method b is only resorted to in cases where a is inadmis- sible. It serves more especially to separate oxide of zinc from other bases. Salts of zinc with organic acids must not be converted into the oxide by ignition, since this process would cause the reduction of a small portion of the oxide to the metallic state, and its dissipation in vapor. 108.] OXIDE OF ZINC. 167 If the acids are volatile, the zinc may be determined at once according to method a ; if. on the contrary, the acids are non-volatile, the zinc may either be precipitated as sulphide, or the salt under examination may be heated to very gentle redness, the residue extracted with nitric acid, and the solution treated according to a or c. The methods of estimating the oxide of zinc in its combinations with chromic acid, phosphoric acid, boracic acid, and silicic acid, will be found in Part II. of this section, \\nder the heads of the several acids. The volume- trical methods are chiefly employed in technical processes. See Special Part. Determination as Oxide of Zinc. a. By Precipitation as Carbonate of Zinc. Heat the moderately dilute solution of the salt of zinc under exami- nation nearly to boiling, in a capacious vessel, best in a platinum dish ; add, drop by drop, carbonate of soda in excess ; boil a few minutes ; let the solid particles subside, decant through a filter, and boil the precipi- tate three times with water, decanting each time ; then transfer the precipitate to the filter, wash completely with hot water, dry, and ignite as directed 53, taking care to have the filter as clean as practicable, before proceeding to incinerate it. Should the solution contain ammoniacal salts, the ebullition must be continued until, upon a fresh addition of the carbonate of soda, the escaping vapor no longer imparts a brown tint to turmeric paper. If the quantity of ammoniacal salts present is considerable, the fluid must be evaporated boilingio drynese. It is, therefore, in such cases more convenient to precipitate the zinc as sulphide (see 6). The presence of a great excess of acid in the solution of zinc must be as much as possible guarded against, that the effervescence from the escaping carbonic acid gas may not be too impetuous. The filtrate must always be tested with sulphide of ammonium, to ascertain whether the whole of the zinc has been precipitated ; a slight precipitate will in- deed invariably form upon the application of this test ; but, if the process has been properly conducted, this is so insignificant that it may be alto- gether disregarded, being limited to some exceedingly slight and im- ponderable flakes, which moreover make their appearance only after many hours' standing (cornp. 77). If the precipitate is more con- siderable, however, it must be treated as directed in b, and the weight of the oxide of zinc obtained added to that resulting from the first process. For the properties of the precipitate and residue, see 77. This method yields pretty accurate results, though the numbers found are in most cases a little below those given by the theoretical calcula- tion, as the precipitation is never absolutely complete, and as particles of the precipitate will always and unavoidably adhere to the filter, which exposes them to the chance of reduction and volatilization during the process of ignition. On the other hand, the results show sometimes also an excess over the numbers theoretically calculated ; this is owing to defective washing, as may be seen from the alkaline reaction which the residue manifests in such cases. It is advisable also to ascertain whether the residue will dissolve in hydrochloric acid without leaving silicic acid; this latter precaution is indispensable in cases where the precipitation has been effected in a glass vessel. 6. By Precipitation as Sulphide of Zinc. 168 PROTOXIDE OF MANGANESE. [ 109. Mix the solution of zinc with ammonia until the precipitate which first forms is redissolved ; add sulphide of ammonium in moderate excess, let the precipitate subside in a warm place, and decant on to a filter, wash the precipitate three times with water containing sulphide of ammonium, each time allowing the solid particles to deposit in a warm place, and decanting ; transfer the precipitate now to the filter, and complete the process of washing with water containing sulphide of ammonium ; put the moist filter with the precipitate in a beaker, and pour over it concentrated hydrochloric acid slightly in excess. Put the glass now in a moderately warm place, until the solution smells no longer of sulphuretted hydrogen ; dilute the fluid with a little water, filter, wash the original filter with hot water, and proceed with the solution of chloride of zinc obtained as directed in a. From a solution of acetate of zinc the metal may be precipitated com- pletely, or nearly so, with sulphuretted hydrogen gas, even in presence of an excess of acetic acid, provided always no other acid be present. The precipitated sulphide of zinc is washed with water impregnated with sulphuretted hydrogen, and, for the rest, treated exactly like the sulphide of zinc obtained by precipitation with sulphide of ammonium. (Compare Experiment No. 69.) Small quantities of sulphide of zinc may also be converted directly into the oxide, by heating in a platinum crucible, with free access of air, to gentle redness at first, then, after some time, to most intense redness. c. By direct Ignition. The salt is exposed, in a covered platinum crucible, first to a gentle heat, finally to a most intense heat, until the weight of the residue remains constant. 109. 2. PROTOXIDE OF MANGANESE. a. Solution. Many of the salts of protoxide of manganese are soluble in water. The pure protoxide, and those of its salts which are insoluble in that menstruum, dissolve in hydrochloric acid, which dissolves also the higher oxides of manganese. The solution of the higher oxides is attended with evolution of chlorine equivalent in quantity to the amount of oxygen which the oxide under examination contains, more than the protoxide of manganese and the fluid, after previous application of heat, is ibund to contain protochloride of manganese. b. Determination. Manganese is weighed either as sulphate of protoxide of manganese, or as protosesquioxide of manganese ( 78). Into the latter form it is converted by precipitation as hydrated protoxide or as carbonate of protoxide, sometimes preceded, in the latter case, by precipitation as sulphide of manganese, or as binoxide of manganese ; or, finally, by direct ignition. If we have to deal with a perfectly definite higher oxide of manganese, free from other bodies evolving chlorine upon boiling with hydrochloric acid, the manganese may be determined also volumetrically and in au indirect way. For the methods of effecting this, see Special Part, under the heading "ANALYSIS OF MANGANESE OKES." We may convert into 109.] PROTOXIDE OP MANGANESE. 169 1. PROTOSESQUIOXIDE OF MANGANESE. a. By Precipitation as Carbonate b. By Precipitation as Hydrated of Protoxide of Manganese. Protoxide of Manganese. All the soluble salts of manga- All the compouuds of manganese, nese with inorganic acids, and all with the exception of its salts witb^ its salts with volatile organic acids ; non- volatile organic acids, also those of its salts which, in- soluble in water, dissolve in hydro- chloric acid with separation of their acid. c. By Precipitation as Sulphide of d. By Separation as Binoxide of All compounds of manganese All compounds of manganese in without exception. a slightly acid solution, especially acetate and nitrate of protoxide of manganese. e. By direct Ignition. All oxygen compounds of man- ganese ; salts of manganese with readily volatile acids, and with organic acids. 2. SULPHATE OF PROTOXIDE OF MANGANESE. All the oxides of manganese, and likewise all its salts with volatile acids, provided no non-volatile substance be present. The method 1, e, is the most simple and accurate, and is therefore preferred to all others, wherever it is admissible. The method 2, is con- venient and expeditious ; but its results are not absolutely accurate. The methods 1, c and d, are resorted to only in cases where the appli- cation of none of the other methods is admissible ; the latter, more espe- cially, to effect the separation of manganese from other metals. 1, a, is generally preferred to 1, b, in cases where the choice is permitted. If the solution of manganese contains sugar or some similar non-volatile organic substance, neither 1, a, nor 1, b, is applicable, and recourse must be had to 1, c. The phosphate and borate of manganese are treated, either according to the directions of 1, b, as the salts precipitated from acid solution by potassa are completely decomposed upon boiling with excess of potassa, or according to the direction of 1, c. The proportion of manganese in the silicate of the protoxide is determined, after the separation of the silicic acid ( 140), according to the directions of 1, a ; for the analysis of chromate of protoxide of manganese, see 130 (chromic acid). The estimation of manganese from the quantity of chlorine dis- engaged upon boiling the oxides of the metal with hydrochloric acid, is resorted to, more particularly, to determine the degrees of oxidation of manganese, and permits also the estimation of manganese in pi'esence of other metals. 1. Determination as Protosesquioxide of Manganese, a. By Precipitation as Carbonate of Protoxide of Manganese. The precipitation and washing are effected in exactly the same way as directed 108, a (determination of zinc as oxide, by precipitation as 170 SULPHATE OF PROTOXIDE OP MANGANESE. [ 109. carbonate) ; the precipitate is dried, and then ignited as directed 53. The lid is removed from the crucible, and the heat maintained at a high degree of intensity, until the weight of the residue remains constant. Care must be taken to prevent reducing gases finding their way into the crucible. For the properties of the precipitate and residue, see 78. *This method, if properly executed, gives accurate results. The principal point is to continue the application of a sufficiently intense heat long enough to effect the object in view. It is necessary also to ascertain whether the residue has not an alkaline reaction, and whether it dis- solves in hydrochloric acid without leaving silica. b. By Precipitation as Hydrated Protoxide of Manganese. Precipitate the solution of the salt under examination in a platinum or silver dish, with solution of pure soda or potassa, and proceed in all other respects as in a. If phosphoric acid is present, or boracic acid, the fluid must be kept boiling for some time with an excess of alkali. FOE the properties of the precipitate, see 78. The method gives accurate results. c. By Precipitation as Sulphide of Manganese. Mix the manganese solution in a flask, with chloride of ammonium, then if the fluid is acid, with ammonia, until the reaction is neutral, or remains only very slightly acid ; add yellow sulphide of ammonium in moderate excess; let the precipitate subside in a warm place; then decant the supernatant fluid through a filter ; wash three times by de- cantation, and, at last, thoroughly, and without interruption, on the filter, with water mixed with a little yellow sulphide of ammonium. Put the moist filter with the precipitate into a beaker, pour dilute hydrochloric acid over it, and warm until the mixture smells no longer of sulphuretted hydrogen ; filter, wash the residuary paper carefully, and proceed with the filtrate as directed in a. d. By Separation as Binoxide of Manganese. Heat the solution of the acetate of protoxide of manganese or some other compound of the protoxide containing but little free acid, after addition of a sufficient quantity of acetate of soda, to from 122 to 140 F., and transmit chlorine gas through the fluid. The whole of the manga- nese present falls down as binoxide (Schiel, Rivot, Beudant, and Daguiri). Wash, first by decantation, then upon the filter ; dry, transfer the preci- pitate to a flask, add the filter ash, heat with hydrochloric acid, filter, and precipitate as directed in a. I cannot recommend the direct con- version of the precipitated binoxide into protosesquioxide by ignition, as that body has an extraordinary tendency to take up alkali. The sepa- ration of manganese as binoxide, by evaporating the solution of the man- ganese compound in nitric acid to dryness, and heating the residue, finally to 311 F., is given in the fifth section. e. By direct Ignition. The manganese compound under examination is introduced into a platinum crucible, which is kept closely covered at first, and exposed to a gentle heat ; after a time the lid is taken off, and replaced loosely on the crucible, and the heat is increased to the highest degree of intensity, with careful exclusion of reducing gases ; the process is continued until the weight of the residue remains constant. The conversion of the higher oxides of manganese into protosesquioxide of manganese requires 110.] PROTOXIDE OF NICKEL. 171 a more intense heat (hardly attainable by any other means than by a gas blowpipe-lamp), and a more protracted application of it than the conver- sion of the protoxide and sesquioxide. In the case of salts of manganese with organic acids, care must always be taken to ascertain whether the whole of the carbon has been consumed j and should the contrary turn out to be the case, the residue must either be redissolved in hydrochloric acid, and the solution precipitated, &c., as directed in a, or it must be repeatedly evaporated with nitric acid, until the whole of the carbon is oxidized. The method, if properly executed, gives accurate results. In the ignition of salts of manganese with organic acids, minute particles of the salt are generally carried away with the empyreumatic products evolved in the process, which, of course, tends to reduce the weight. 2. Determination as Sulphate of Protoxide of Manganese. The same method as in the case of magnesia under the same circum- stances ; see 104, 6, 1. Care must be taken, more particularly, to expose the residue to a faint red heat only, and to avoid too great an excess of sulphuric acid. For the properties of the residue, see 78. The results are generally a little too low, as a minute quantity of sulphuric acid is apt to escape if the heat applied exceeds faint redness. no. 3. PKOTOXIDE OF NICKEL. a. Solution. Many of the salts of protoxide of nickel are soluble in water. The pure protoxide, in its common modification, ani those of its salts which are insoluble in water, dissolve, without exception, in hydrochloric acid. The peculiar modification of protoxide of nickel, discovered by Genth, which crystallizes in octahedra, does not dissolve in acids, but is rendered soluble by fusion with bisulphate of potassa. Metallic nickel dissolves slowly, with evolution of hydrogen gas, when warmed with dilute hydro- chloric or sulphuric acid; in nitric acid, it dissolves with great readiness. Sulphide of nickel is but sparingly soluble in hydrochloric acid, but it dissolves readily in nitrohydrochloric acid. Peroxide of nickel dissolves in hydrochloric acid, upon the application of heat, to protochloride, the solution being attended with evolution of chlorine. b. Determination. Protoxide of nickel is always weighed as such ( 79). The compounds of nickel are converted into the pure protoxide, either by precipitation as hydrated protoxide, preceded, in some instances, by precipitation as sulphide of nickel, or by ignition. We mav convert in to ' e may convert into PROTOXIDE OF NICKEL. a. By Precipitation as Hydrated b. By Precipitation as Sulphide Protoxide of Nickel. of Nickel. All the salts of nickel with in- All compounds of nickel without organic acids which are soluble in exception, water, and all its salts with volatile organic acids; likewise all salts of nickel which, insoluble in water, dis- solve in the stronger acids, with se- paration of their acid. 172 PROTOXIDE OP NICKEL. [ 110. c. By Ignition. The salts of nickel with organic acids, and with readily volatile oxygen acids, or with such oxygen acids as are de- composed at a high temperature (carbonic acid, nitric acid). The method c, when it is applicable, is preferable to the other methods, more especially in the case of salts of nickel with the inorganic acids pointed out in c. The method a is most frequently resorted to. If sugar or some other non-volatile organic substance is present, this must either be destroyed by ignition before proceeding to the solution and precipitation of the compound under examination, or the method b, of which the application otherwise is almost exclusively con- fined to effect the separation of the protoxide of nickel from other bases, must be resorted to. The methods of estimating the protoxide of nickel in its combinations with chromic acid, phosphoric acid, boracic acid, and silicic acid, will be found in Part II. of this section, under the heads of the several acids. Determination as Protoxide of Nickel. a. By Precipitation as Hydrated Protoxide of Nickel. Mix the solution with pure solution of potassa or soda in excess, heat for some time nearly to ebullition, decant 3 or 4 times, filter, wash the precipitate thoroughly with hot water, dry and ignite ( 53). The best vessel to effect the precipitation in is a platinum dish ; in presence of nitrohydrochloric acid, or, if the operator does not possess a sufficiently capacious dish of that metal, in a porcelain dish ; glass vessels do not answer the purpose so welL Presence of ammoniacal salts, or of free ammonia, does not interfere with the precipitation. For the properties of the precipitate and residue, see 79. This method, if properly executed, gives very accurate results. The thorough washing of the precipitate is a most essential point. It is necessary also to ascertain whether the residue has not an alkaline reaction, and whether it dissolves completely in hydrochloric acid. b. By Precipitation as Sulphide o/NickeL This requires the greatest care and attention. The best way is to proceed according to either of the two subjoined methods. a. The moderately dilute solution of nickel is, if necessary, neutralized with ammonia (the reaction should be rather slightly acid than alkaline) : colorless perfectly saturated hydrosulphate of sulphide of ammonium is then added as long as a precipitate continues to form, care being taken, however, not to add the reagent in too considerable excess. The mixture is now well stirred, passed on to a moistened filter, atul the precipitate thoroughly washed by a continuous stream of distilled water, to which one or two drops of colorless perfectly saturated hydrosulphate of sulphide of ammonium have been added. The filtrate washings and the rinsing water must be perfectly colorless. The precipitate is then dried in the funnel, and subsequently removed as completely as possible from the filter, and transferred to a beaker ; the filter is incinerated in a coil of platinum wire, or upon the lid of a crucible, and the a.sh added to the dry precipitate. The precipitate is now treated with con- centrated nitrohydrochloric acid, and the mixture digested at a gentle heat, until the whole of the sulphide of nickel is dissolved, and the undissol-ved sulphur appears of a pure yellow ; the fluid is then diluted, filtered, and the nitrate precipitated, As the separation of the bases from the large excess of molybdic acid used is somewhat tedious, the best way is to arrange matters so that this process may be altogether dispensed with. Supposing, for instance, you have a fluid containing sesquioxide of iron, alumina, and phosphoric acid, estimate, in one portion, by cautious precipitation with ammonia, the total amount of the three bodies ; in another portion the phosphoric acid, by means of molybdic acid ; and in a third, the sesquioxide of iron, bv the volumetrical method ( 113, 2, a). The difference gives the alumina. 136. 2. BORACIC ACID. I. Determination. The determination of boracic acid is effected either in an indirect way, or in form of borofluoride of potassium. 1. The determination of the boracic acid in an aqueous or alcoholic solution cannot be effected by simply evaporating the fluid and weighing the residue, as a notable portion of the acid volatilizes and is carried off with the aqueous or alcoholic vapor. This is the case also when the solution is evaporated with oxide of lead in excess. The best way of determining the boracic acid is therefore the follow- ing : Mix the solution of the boracic acid with a weighed quantity of pure carbonate of soda,* varying in amount from about equal to the supposed quantity of the boracic acid present to double that amount. Evaporate * Fused carbonate of soda answers the purpose best. 136.] BORACIC ACID. 255 the mixture to dryness, heat the residue to fusion, and weigh. The residue contains a known amount of soda, and unknown quantities of carbonic acid and boracic acid. Determine the carbonic acid by one of the methods given in 139, and calculate the boracic acid from the difference (H. Rose). 2. If boracic acid is to be determined as borofluoride of potassium, no bases except alkalies must be present. The process which succeeds best if potassa alone is present is conducted as follows : Mix the fluid with pure solution of potassa, adding for each equivalent of boracic acid supposed to be present, at least 1 equivalent of potassa ; add pure hydro- fluoric acid (free from silicic acid) in excess, and evaporate, in a platinum basin, on the water-bath, to dryness. The hydrofluoric acid must be applied in sufficient quantity to let a portion of it escape in the pro- cess of evaporation, so that the evaporating fumes redden litmus paper. The residue consists now of K Fl, B F1 3 and K Fl, H Fl. Treat the dry saline mass, at the common temperature, with a solution of 1 part of acetate of potassa in 4 parts of water, let it stand a few hours, with fre- quent stirring, then decant the fluid portion on to a weighed filter, and wash the precipitate repeatedly in the same way, and finally on the filter, with solution of acetate of potassa, until the last rinsings are no longer precipitated by chloride of calcium. By this course of proceed- ing, the hydrofluoride of potassium is removed, without a particle of the borofluoride of potassium being dissolved. To remove the acetate of potassa, wash the precipitate now with spirit of wine of 84 Tralles, dry at 212 F., and weigh. As chloride of potassium, nitrate and phosphate of potassa, salts of soda, and even sulphate of potassa, though the latter salt with some difficulty, dissolve in solution of acetate of potassa, the presence of these salts does not interfere with the estimation of the boracic acid ; however, salts of soda must not be present in considerable proportion, as fluoride of sodium dissolves with very great difficulty. The results obtained by this method are satisfac- tory, titroineyer's experiments gave from 97 '5 to 100 '7, instead of 100. For the composition and properties of borofluoride of potassium, see 93, 5. As the salt is very likely to contain silicofluoride of barium, it is indispensable to test it first for that substance ; this is done by placing a small sample of it on moist blue litmus paper, and putting another sample into cold concentrated sulphuric acid. If the blue paper turns red, and effervescence ensues in the sulphuric acid, the salt is impure, and contains silicofluoride of potassium. To remove this impurity, dissolve the remainder of the salt, after weighing it again, in boiling water, add ammonia, and evaporate, and repeat the same operation at least four times. Finally, after warming once more with ammonia, filter off the silicic acid, evaporate to dryness, and treat again with solution of acetate of potassa and alcohol (A. /Stromeyer, "Anna!, d. Chem. u. Pharm.," 100, 82). I have, however, slightly modified Stromeyer s method for effecting the separation of the silicic acid, the results of my experiments having convinced me that treating the salt only once with ammonia, as recommended by that chemist, is not sufficient to effect the object in view. II. Separation of Boracic Acid from the Bases. a. From the Alkalies. Dissolve a weighed quantity of the borate in water, add an excess of hydrochloric acid, and evaporate the solution on the water-bath. ,256 BORACIC ACID. [ 136. Towards the end of the operation add a few more drops of hydro- chloric acid, and keep the residue on the water-bath, until no more hydrochloric acid vapors escape. Determine now the chlorine in the residue ( 141), calculate from this the alkali, and the boracic acid from the difference. E. Schweizer, with whom this method originated, states that it gave him very satisfactory results in his analysis of borax. It will, probably, answer also for the estimation of the bases in the case of some other boratea. It is self-evident that the boracic acid may, in such cases, be estimated, in another portion of the salt, by I., 2. If you have to estimate boracic acid in presence of large proportions of alkaline salts, make the fluid alkaline with potassa, evaporate to dryness, extract the residue with alcohol and some hydrochloric acid, add solution of potassa to strongly alkaline reaction, distil off the spirit of wine, and then proceed as iu I., 2 (Aug. Stromeyer, "Annal. d. Chem. u. Pharm.," 100, 82). b. From almost all other Bases. The compounds are decomposed by boiling or fusion with carbonate of potassa or hydrate of potassa ; the precipitated base is filtered off, and the boracic acid determined in the filtrate, according to the directions of I., 2. If magnesia was present, a little of this is very likely to get into the filtrate ; upon neutralizing with hydrofluoric acid, this separates as insoluble fluoride of magnesium, which may either be filtered off at once, or removed subsequently, by treating the borofluoride of potas- sium with boiling water, in which that salt is soluble, the fluoride or magnesium insoluble. c. From the Metallic Oxides of the Fourth, Fifth, and Sixth Groups. The metallic oxides are precipitated by sulphuretted hydrogen, or, as the case may be, sulphide of ammonium, and determined by the appro- priate methods. The quantity of boracic acid may often be inferred from the loss. If it has to be estimated in the direct way, the filtrate, after addition of solution of potassa and some nitrate of potassa, is evaporated to dryness, the residue heated to redness, and the boracic acid estimated by I., 2. In cases where the metal has been pre- cipitated by sulphuretted hydrogen from acid or neutral solutions, the boracic acid may also be determined in the filtrate, by the method given in I., 1, after being first completely freed from sulphuretted hydro- gen by transmitting carbonic acid through the fluid. d. From tlie whole of the Fixed Bases. A portion of the very finely pulverized compound under examination is weighed, put into a capacious platinum crucible, and digested with a sufficient quantity of hydrofluoric acid ; pure concentrated sulphuric acid is then gradually added, drop by drop, and the mixture heated, gently at first, then more strongly, until the excess of the sulphuric acid is completely expelled. In this operation the boracic acid goes off in the form of fluoride of boron (Bo O 3 + 3 H Fl = B F1 3 + 3 HO). The residue contains the bases in the form of sulphates ; the bases are de- termined by the appropriate methods, and the quantity of the boracic acid is inferred from the difference between the weight of the separated base and that of the analysed borate. The application of this method presupposes, of course, that the analysed compound is decomposable by sulphuric acid. 137.] OXALIC ACID. 257 137. 3. OXALIC ACID. I. Determination. Oxalic acid is either precipitated as oxalate of lime, and the latter determined as carbonate of lime; or the amount contained in a com- pound is inferred from the quantity of solution of permanganate of potassa required to effect its conversion into carbonic acid ; or from the quantity of gold which it reduces ; or from the amount of carbonic acid which it produces upon accession of 1 equivalent of oxygen. a. Determination as Carbonate of Lime. Precipitate with solution of acetate of lime, added in moderate excess, and treat the precipitated oxalate of lime as directed in 103. If this method is to yield accurate results, the solution must be neutral or made slightly acid by acetic acid; it must not contain alumina, sesquioxide of chromium or oxides of the heavy metals, more especially sesquioxide of iron or oxide of copper ; therefore, where these conditions do not exist, they must first be supplied. b. Determination by means of Solution of Permanganate of Potassa. Determine the strength of the solution of permanganate of potassa, as directed 1 1 2, 3, a, cc, by means of oxalic acid ; then dissolve the com- pound in which the oxalic acid is to be estimated, and which must be free from all other bodies that might act on solution of permanganate of potassa, in 400 or 500 parts of water, or, as the case may be. acid and water; add, if necessary, a further, not too small, quantity of sulphuric acid, or hydrochloric acid, heat to about 140 F., and then add solution of per- manganate of potassa, drop by drop, with constant stirring, until the fluid just shows a red tint (compare 112, 2, a, cc). Knowing the quantity of oxalic acid which 100 cubic centimetres of the standard solution of permanganate of potassa will oxidize, a simple calculation will give the quantity of oxalic acid corresponding to the cubic centimetres of solution of permanganate of potassa used in the experiment. The results are very accurate (compare Experiment No. 66). c. Determination by inference from the amount of Gold reduced by tlie Acid (H. Rose}. a. In Compounds soluble in Water. Add to the solution of the oxalic acid or the oxalate a solution of sodio-terchloride, or ammonio-terchloride of gold, and digest for some time at a temperature near ebullition, with exclusion of direct solar light. Collect the precipitated gold on a filter, wash, dry, ignite, and weigh. 1 equivalent of gold (19 6 '67) corresponds to 3 equivalents of C O (3x36 = 108). /3. In Compounds insoluble in Water. Dissolve in the least possible amount of hydrochloric acid, dilute with a very large quantity of water, in a capacious flask, cleaned previously with solution of soda; add solution of gold in excess, boil the mixture some time, let the gold subside, taking care to exclude solar light, and then proceed as directed in a. d. Determination as Carbonic Acid. This may be effected either, a. By the method of organic analysis ( 175); or, 258 HYDROFLUORIC ACID. [ 138. /3. By mixing the oxalic acid or oxalate with finely pulverized binoxide of manganese in excess, and adding sulphuric acid to the mixture, in an apparatus so constructed that the disengaged carbonic acid passes off perfectly dry. The theory of this method may be illustrated by the following equa- tion : C !! 8 + Mn 2 + S O a = Mn 0, S 3 + 2 C 0, For each equivalent of oxalic acid we obtain accordingly 2 equi- valents of carbonic acid. For the apparatus and process, I refer to the chapter on the examination of manganese ores, in the special part of this work. Here I may remark that free oxalic acid must first be prepared for the process by slight supersaturation with ammonia, and also that 9 parts of anhydrous oxalic acid require theoretically 11 parts of pure binoxide of manganese. Since an excess of the latter substance does not interfere with the accuracy of the results, it is easy to determine the amount to be added. The binoxide of manga- nese need not be pure, provided it contains no carbonate. This method is very expeditious, and gives accurate results, if the process is con- ducted in an apparatus sufficiently light to admit of the use of a delicate balance. Instead of binoxide of manganese, chromate of potassa may be used ; compare 130, c. II. Separation of Oxalic Acid from the Bases. The most convenient way of analysing oxalates is, in all cases, to determine in one portion, the acid, by one of the methods given in I., in another portion, the base, particularly as the latter object may be effected by simple ignition in the air, which reduces the salt either to the metallic state (e.g., oxalate of silver), or to pure oxide (e.g., oxalate of lead), or to carbonate (e.g., the oxalates of the alkalies and alkaline earths). If acid and base have to be determined in one and the same portion of the oxalate, the following methods may be resorted to : a. The oxalic acid is determined by I., c, and the gold separated from the bases in the filtrate by the methods given in Section V. b. In many soluble salts the oxalic acid may be determined by the method I., a; separating the bases afterwards from the excess of the salt of lime by the methods given in Section V. c. All oxalates whose bases are precipitated by carbonate of potassa or carbonate of soda, and are insoluble in an excess of the precipitant, may be decomposed by boiling with an excess of solution of carbonate of potassa or carbonate of soda, into oxide or carbonate on the one, and alkaline oxalate on the other side. d. All salts of oxalic acid with the oxides of the fourth, fifth, and sixth groups may be decomposed with sulphuretted hydrogen, or with sulphide of ammonium. 138. 4. HYDROFLUORIC ACID. I. Determination. Free hydrofluoric acid in aqueoxis solution is best determined as fluoride of calcium. For this purpose, carbonate of soda is added in moderate excess, then a solution of chloride of calcium as long as a pre- cipitate continues to form ; when the precipitate, which consists of fluoride 138.] HYDROFLUORIC ACID. 259 of calcium and carbonate of lime, has subsided, it is washed, first by decantation, afterwards on the filtei', and dried ; when dry, it is ignited in a platinum crucible ( 53); water is then poured over it, in a platinum or porcelain dish, acetic acid added in slight excess, the mixture eva- porated to dryness on the water-bath, and heated on the latter until all odor of acetic acid disappears. The residue, which consists of fluoride of calcium and acetate of lime, is treated with water, the fluoride of calcium filtered off, washed, dried, ignited ( 53), and weighed. If the precipitate of fluoride of calcium and carbonate of lime were treated with acetic acid, without previous ignition, the washing of the fluoride would prove a difficult operation. Presence of nitric or hydrochloric acid in the aqueous solution of the hydrofluoric acid does not interfere with the process (H. Rose). II. Separation of Fluorine from the Metals. a. Soluble Fluorides. If the solutions have an acid reaction, carbonate of soda is added in excess. If this produces no precipitate, the fluorine is determined by the method given in I., and the bases in the filtrate are separated from the excess of lime, and from the soda, by the methods given in Section V. But if the carbonate of soda produces a precipitate, the mixture is heated to boiling, then filtered, and the fluorine determined in the filtrate by the method given in I., the base is in the residue, which must, how- ever, first be tested, to make sure that it contains no fluorine. Neutral solutions are mixed with a sufficient quantity of chloride of calcium, and the mixture heated to boiling, in a platinum dish or, but less appropriately, in a porcelain dish ; the precipitate of fluoride of cal- cium is allowed to subside, thoroughly washed with hot water, by decantation, transferred to the filter, dried, ignited, and weighed. The bases in the filtrate are then separated from the excess of the salt of lime by the usual methods. That the bases may be determined also in separate portions by the methods given in b, need hardly be stated. b. Insoluble Fluorides. , a. Anhydrous insoluble Fluorides. The finely pulverized and accurately weighed substance under ex- amination is heated for some time with concentrated pure sulphuric acid, and the residue finally ignited until the free sulphuric acid is completely expelled. The residuary sulphate is weighed, and the metal contained in it calculated. The difference between the calculated -weight of the metal and that of the original fluoride shows the amount of fluorine originally present in the analysed compound. In cases where we have to deal with metals whose sulphate gives off part of the sulphuric acid upon ignition, or where the residue contains several metals, it is necessary to subject the residue to a further analysis before this calculation can be made. ft. Hydrated insoluble Fluorides. A sample of the compound under examination is heated in a tube, aa. The Water expelled is perfectly neutral to Litmus Paper. In this case the amount of water present is ascertained by igniting the hydrated compound, and the fluorine and metal are subsequently deter- mined as directed in II., b, a. s 2 260 CARBONIC ACID. [ 139, bb. The Water expelled has an acid reaction. The fluoride under examination is, in the first place, treated with, sulphuric acid as directed in TL, 6, a, to determine the metal on the one hand, and the water + fluorine on the other. Another weighed por- tion is then mixed, in a small retort, with about 6 pai-ts of recently ignited oxide of lead ; the mixture is covered with a layer of oxide of lead, the retort weighed, and the water (which is now entirely free from admixture of hydrofluoric acid) expelled by the application of heat, increased gradually to redness. The weight of the expelled water is inferred from the loss. The first operation having given us the exact amount of water + fluorine, the quantity of the latter substance may now be readily calculated, by simply subtracting from the combined weight of the water + fluorine, the weight of the water expelled in the second operation. In the fifth section we shall have occasion to speak of another method of determining fluorine (in the chapter on the separation of fluorine from silicic acid). Fourth Division of the First Group of the Acids. CARBONIC ACID SILICIC ACID. 139. 1. CARBONIC ACID. I. Determination. a. In a mixture of Gases. Measure the gases accurately, in a graduated tube over mercury, insert into the tube a moistened ball of hydrate of potassa, cast on a platinum wire in a pistol bullet-mould, and leave this in the tube for 24 hours, or until the volume of the gas ceases to show further diminution ; withdraw the ball, and measure the gas remaining ; the amount of carbonic acid gas originally present is inferred from the difference, pro- vided the gaseous mixture contained no other gas liable to absorption, by potassa (compare also, 13-16). b. In Aqueous Solution. a. Mix solution of chloride of barium or chloride of calcium* with, solution of ammonia in excess, heat the mixture to boiling, let the pre- cipitate deposit, and then filter. Have ready several flasks of about 300 cubic centimetres capacity each, provided with tight-fitting corks, and pour into each about 50 c.c. of the filtrate. The method to be adopted for adding, without loss of gas, certain definite quantities of solution of carbonic acid to the filtrate in the flasks, depends upon whether the carbonic acid water is contained in a stone bottle, or flowing from a pipe, or whether it can be taken directly from the spring. In the former case weigh the flasks, with the ammoniacal chloride of barium solution in them, separately, together with the cork ; then let the water run into each flask, with proper care, until nearly full,f cork instantly, * Solution of chloride of barium is preferable in cases where the after process is to be conducted according to aa ; solution of chloride of calcium in cases where bb to be resorted to. f If the carbonic acid water is in a stone bottle, it should always be transferred to the flask by means of a siphon, after being cooled first to about 39'2 F. If the water were poured in direct from the bottle, some carbonic acid gas might also find its way into the flask, together with the water. 139.] CARBONIC ACID. 261 and weigh again ; this will give the exact quantity of water con- tained in each flask. Or, pour into each flask, in the first instance, exactly 50 cubic centimetres of the ammoniacal solution of chloride of barium, or chloride of calcium, then fill in the water, in the way just stated, mark with a diamond, or by means of a small paper slip pasted on the outside of the flask the point to which it reaches ; measure afterwards the contents of the flask up to the mai'k, and deduct the 50 cubic centimetres of chloride of barium or chloride of calcium solu- tion, when the difference will show the quantity of carbonic acid water added. In the latter case, where the water can be taken direct from the spring, you will find the estimation of the volume more convenient by making use of a siphon or large pipette, dipped into the spring, so that the water enters through the lower orifice. The siphon or pipette used for the piirpose must have a mark cut in the glass a little below the upper orifice ; the exact volume which it holds up to this mark may be determined either before or after the operation, by filling it with water up to the mark, and measuring in a graduated glass. When the siphon or pipette is quite full, lift it out of the spring, wipe the outside dry, with proper expedition ; let some water flow out, until the contents reach just up to the mark ; then empty into one of the flasks containing the ammouiacal solution of chloride of barium, or chlo- ride of calcium, and cork instantly. Proceed in the same way with the other flasks. The ammeniacal chloride of barium or chloride of calcium solution in the flasks generally turns turbid as soon as the carbonic acid water is poured in ; but, it is only after standing some time on the water bath, or even after actual ebullition, that the whole of the carbonic acid separates in form of carbonate of baryta or carbonate of lime.* When this point has been attained, allow the precipitate to subside, with ex- clusion of air, and then proceed by one of the following methods : aa. Estimation of the Carbonic Acid by the Gravimetrical MetJiod. Decant the supernatant fluid rapidly on to a filter, secluded as much as possible from access of air ; fill the flask with warm water, and insert the cork ; shake, let the* solid particles deposit, decant again, and repeat this washing by decantation once more; transfer the precipitate now to the filter, wash until the last rinsings remain clear upon addition of solution of nitrate of silver, dry, ignite gently, and weigh ( 101, 2, a). The amount of the carbonic acid may now be calculated from the weight of the carbonate of baryta, provided the analysed solution contained, besides carbonic acid, no other substance liable to be precipitated by ammonia aud chloride of barium. But should the latter be the case, and the precipitated carbonate of baryta contain an admixture of carbonate of lime, phosphate of baryta, ses- quioxide of iron, or other similar substances, the carbonic acid must be determined in the gently ignited, but not weighed precipitate, as directed in II., d. The filter, freed as completely as possible from adhering matter, should be incinerated, and the ashes added to the precipitate. If the quantity of the precipitate is very large, it is best first to weigh the * The tardiness of this reaction is explained, as is well known, upon the assumption that carbonic acid and ammonia, coming in contact, form, in the first place, carbamate of ammonia, CO, + 2NH, *fl tfl 262 CARBONIC ACID. [ 139. whole of it, and then to determine the carbonic acid in a weighed portion of the uniformly mixed powder. If the last particles of the precipitate cannot be removed from the flask by mechanical means, they are dissolved in a little dilute hydro- chloric acid (the glass having previously been thoroughly washed), the solution is precipitated with carbonate of soda, and the trifling precipi- tate formed filtered off on a separate small filter, which is incinerated with the larger one. bb. Estimation of the Carbonic Acid by the Volumetrical Method. Filter as in aa ; there is no necessity, however, to collect the whole of the precipitate on the filter, as the last particles adhering to the inside of the flask may be left and washed by decantation. Put the funnel with the filter containing the precipitate on the flask in which the precipitation has been effected, make a small hole in the point of the filter, and rinse the thoroughly washed precipitate into the flask, with the aid of a washing bottle. Dry the filter, incinerate, and add the ash to the precipitate in the flask. Add now a little tincture of litmus, and then, from a Mohrs burette (see 21), standard (or, according to cir- cumstances, decimal standard) nitric or hydrochloric acid, until the fluid shows a distinct red color ; expel the carbonic acid by heat, and then add solution of soda of known strength until the fluid just appears blue. After noting the number of cubic centimetres of the acid and soda, add again about 1 cubic centimetre of acid, and, after heating to boiling, solution of soda until the fluid again just appears blue. This operation may be repeated several times. By subtracting the volume of acid corresponding to the volume of solution of soda used in the process from the entire volume of acid added in the several experiments, you find the quantity of acid which has served to expel from the carbonate of baryta the carbonic acid, and is accordingly equivalent to the latter. For the details of this expeditious and very accurate method, see 223. As the coloring matter of the litmus is sometimes thrown down, along with silicic acid separating from the precipitate, it is occasionally finind necessary to add again some tincture of litmus. If this should fail to lead to the desired result, sohition of soda is added until the reaction is almost complete ; the amount of the soda solution left in the burette is then read off, the fluid diluted to a certain definite volume, and filtered ; one-half the volume taken of the clear filtrate and solution of soda very cautiously added until the fluid appears blue ; the quantity of soda solu- tion required to effect this purpose is then doubled, and the result added to the quantity first used. ft. In cases where rigorously accurate results are not required, and it is simply wished to ascertain approximately and comparatively the amount of free carbonic acid in a mineral water, R. Kersting's method (" Annal. d. Chem. u. Pharm.," 94, 112,) maybe resorted to. This method is based upon the fact that tincture of litmus is colored violet by free car- bonic acid, but not by bicarbonate of soda. If, therefore, to a solution of carbonate of soda, colored blue by litmus, dilute sulphuric acid is cautiously added, the fluid will acquire a violet tint as soon as Na O, S O s and Na O, 2 C O 2 have been formed in it, and another drop of sulphuric acid is added, which disengages some carbonic acid. The experiment requires, a, standard solution of dilute sulphuric acid, con- taining in 1 cubic centimetre 10 milligrammes of S O t , corresponding to 1 1 milligrammes of carbonic acidj this is prepared by mixing 1 volume 139.] CARBONIC ACID. 263 of standard sulphuric acid ( 215) with 3 volumes of water; b, a concen- trated solution of soda containing some carbonic acid, as is, moreover, usually the case. aa. Add to about 450 cubic cent, of pure water 1^ cub. cent, of tincture of litmus, prepared by digesting in the cold equal parts of litmus and water ; add exactly 5 c.c. of the solution of soda, dilute with water to 500 c.c. of fluid; take out, by means of the pipette, 3 several portions of 100 c.c. each, pour them respectively into 3 beakers, standing on a white ground, and add to each successively, with proper care, dilute standard sulphuric acid, until the color appears distinctly violet. The experiment must be made in the daytime, and by a good light ; towards the termination of the process, you must always wait 1 or 2 minutes after each addition of acid, to allow the change of color to become dis- tinctly visible. Bestow increased care and attention upon the experiment with the fluid in the second beaker, and in the third. Multiply by 5 the volume of acid used in the most accurate of the three experiments, and mark the result as the quantity of acid corresponding to 5 c.c. of the concentrated solution of soda. bb. Add to about 450 to 500 cubic centimetres of the carbonic acid water under examination, carefully measured, either before the experi- ment or after, 5 c.c. of the soda solution b,* and mix. Of this mixture, which is genei'ally tui'bid, owing to the separation of carbonates of alkaline earths, take out successively 3 several portions of 100 c.c. each, add to each portion 4 drops of litmus tincture, and then, cautiously and with stirring, sulphuric acid, until the fluid shows a violet tint. Bestow increased care and attention upon the experiment with the second portion and with the third. By determining now the quantity of carbonic acid water used, if you have not done so before, you find the last factor still required for calculating the results. Suppose the experiment has been made with 455 c.c. of mineral water, and you have added to this 5 c.c. of solution of soda; 100 c.c. of your mixture required 6 c.c. of sulphuric acid ; 460 c.c. would, accordingly, have required 27 '5 c.c. Now suppose 5 c.c. of soda solution have required 90 - 6 c.c. of acid, the 455 c.c. of the carbonic acid water contained, accordingly, as much free carbonic acid as corresponds to 90'6 27'6 = 63 c.c. of sulphuric acid, that is to say, 63 x O'Oll = - 693 grammes ; as for every 2 equivalents of carbonic acid, which are ultimately present in the fluid in the state of bicarbonate of soda, there is required 1 equivalent less of sulphuric acid ; 1 equivalent of S O 3 = 40 corresponds, consequently, to 2 equivalents of C O 2 = 44, or 10 milligrammes S O z (i.e. the quantity con- tained in 1 c.c.) correspond to 11 milligrammes C O 2 . To obtain properly corresponding results by this method requires a practised eye ; the method has, therefore, rather a subjective than an objective value; and, in my opinion, ought never to be employed in cases intended for publication. II. /Separation of Carbonic Acid from tlie Bases, and its estimation in Carbonates, a. Separation from Alkalies. aa. If the salts contain 1 equivalent of carbonic acid to 1 equivalent * If the water is in a bottle, cool it down to about 39-2 F., then remove the stopper, take out a little of the water, and instantly add the solution of soda. If 5 c.c. is not sufficient to make the water alkaline, add 10 c.c. 264 CARBONIC ACID. [ 139. of base, and there is no other salt with alkaline reaction present, the most convenient way is to determine the quantity of the base by the alkalimetrical method ( 219, 220), and to calculate for each equiva- lent of base 1 equivalent of carbonic acid. bb. If the salt contains more than 1 equivalent of carbonic acid to 1 equivalent of base, mix the solution of a weighed portion with a mixture of chloride of barium, or chloride of calcium and ammonia, heated to boiling and filtered, and proceed exactly as directed in I., b, a. cc. If the salts contain less than 1 equivalent of carbonic acid to 1 equivalent of base, mix the dilute solution of a weighed portion with an excess of pure and neutral solution of chloride of barium or chloride of calcium ; heat, let deposit, and treat the washed precipitate as in I., b, a, aa, or bb. b. From the Alkaline Earths. If the compounds are neutral and contain no other acids forming with the alkalies salts with alkaline reaction, the bases in them may be deter- mined by the alkalimetrical method ( 223), and 1 equivalent of car- bonic acid reckoned for each equivalent of base. c. Separation of Carbonic Acid from Bases which upon Ignition readily and completely yield the Carbonic Acid ivith which they are combined. Such are, for instance, the carbonates of the oxides of zinc, cadmium, lead, copper, magnesium, &c. a. Anhydrous Carbonates. Heat the weighed substance, in a platinum crucible (carbonates of cadmium and lead in a porcelain crucible), to ignition, and keep in that state until the weight of the residue remains constant. The results are, of course, very accurate. Substances liable to absorb oxygen upon ignition in the air are ignited in a bulb-tube, through which a stream of dry carbonic acid gas is conducted during the process. The carbonic acid is inferred from the loss. /3. Hydrated Carbonates. The substance is ignited in a bulb-tube through which dried air or, in presence of oxidizable substances, carbonic acid is transmitted, and which is connected with a chloride of calcium tube, by means of a dry, close-fitting cork. During the ignition, the posterior end of the tube is, by means of a small lamp, kept sufficiently hot to prevent the conden- sation of water in it, care being taken, however, to guard against burning the cork. The loss of weight of the tube gives the amount of the water + the carbonic acid ; the increase of weight gained by the chloride of calcium tubes gives the amount of the water, and the difference accor- dingly that of the carbonic acid. A somewhat wide glass tube may also be substituted for the bulb tube, and the substance introduced into it in a little boat, which is weighed before and after the operation. d. Separation of Carbonic Acid from all Bases witlwut exception, in Anhydrous Carbonates. The carbonate under examination is weighed in a platinum crucible, and about 4 times its weight of fused biborate of soda ( 64, 6) added, which has been heated again just previous to weighing. The mix- ture is weighed, and heat is then applied, which is gradually increased to intense ignition, and maintained at this temperature until the contents of the crucible are in a state of calm fusion. The crucible is now 139.] CARBONIC ACID. 265 allowed to cool, and, when cold, weighed. The loss of weight indicates the amount of carbonic acid originally present in the ignited compound. The results are very accurate (SchaffgottscJi). e. From all Bases without exception, no matter whether the Compounds are anhydrous or not. a. Estimation of the Acid from the loss of weight. aa. Carbonates whose Bases form Soluble Salts with Sulphuric Acid. The process is conducted in the apparatus illustrated by Fig. 66. The size of the flasks depends upon the capacity of the balance which the operator possesses. The tube a is closed at b by means of a small wax stopper ;* the other end of the tube a is open, as are also both ends of c and d. The flask B is nearly half filled with concentrated sulphuric acid ; the tubes a, c, and d, must fit air-tight in the per- forations of the corks, and the latter equally so in the mouths of A and B. A weighed portion of the carbonate under examination is put into A ; this flask is then filled about one-third with water, the cork properly inserted, and the apparatus placed in equilibrium upon the balance. A few bubbles of air are now sucked out of d, by means of a small india-rubber tube. This serves to rarefy the air in A also, and causes the sulphuric acid in B to ascend in the tube c. The latter is watched for some time, to ascertain whether the column of sulphuric acid in it remains stationary, which is a proof that the apparatus is air-tight. Air is then again sucked out of d, which causes a portion of the sulphuric acid to flow over into A. The carbonate in the latter flask is decomposed by the sulphuric acid, and the liberated carbonic acid, completely dried in its passage through the concentrated sulphuric acid in B, escapes through d. When the evolution of the gas slackens a fresh portion of sulphuric acid is made to pass over into A, by renewed suction through d ; and the same operation is repeated until the whole of the carbonate is decomposed. A more vigorous suction is now applied, to make a larger amount of sulphuric acid pass over into A, whereby the contents of that flask are considerably heated ; when the evolution of gas bubbles has completely ceased, the wax stopper on a is opened, or the glass rod removed from the india-rubber cap, and suction applied to d, until the air sucked out tastes no longer of carbonic acid.t The apparatus is allowed to cool and then replaced upon the balance, and the equilibrium restored by additional weights. The sum of the weights so added indicates the amount of carbonic acid originally present in the analysed compound. * Or with a small piece of india-rubber tube, drawn over it, and having inserted in the other end a short piece of glass rod. + In accurate experiments, it is advisable to connect the end b of the tube a with a chloride of calcium tube during the process of suction. 266 CARBONIC ACID. [ 139. If the flasks A and B are selected of small size, the apparatus may be so constructed that, together with the contents, it need not weigh above seventy grammes, admitting thus of being weighed on a delicate balance. The results obtained by the use of this apparatus, first sug- gested by Will and Fresenius, are very accurate, provided the quantity of the carbonic acid be not too trifling. I have not yet been able to convince myself that any of the proposed modifications of this apparatus affords essential advantages. For the mode of proceeding in cases where the carbonate is mixed with a metallic sulphide or chloride, I refer to Section Y. bb. Carbonates wJwse Bases form insoluble Salts with Sulphuric Acid. The analysis of such carbonates cannot well be effected by the method aa, as the insoluble sulphate formed (sulphate of lime, for instance) par- tially protects the yet undecomposed portion of the carbonate from decomposition. The apparatus is therefore modified as shown in Fig. 67. It will be seen from the engraving that the modification consists simply in the tube a, b, being expanded at the upper end into a bulb, and drawn out to a fine point at the lower end. The process is conducted as follows : A weighed portion of the carbonate is put into A, which flask is filled about one-third with water. The bulb- tube a contains an amount of dilute nitric acid, more than sufficient for the decomposition of the carbonate, and which is prevented from flowing through the narrow aperture of this tube by the little wax stopper b.* The point of this tube must not dip into the water in A. The apparatus, having been put in equilibrium on the balance, the tube a is carefully and cautiously moved down, until its point nearly touches the bottom of A. The wax stopper b is then momentarily raised, or the glass rod removed from the india-rubber cap, so as to allow a small quantity of nitric acid to flow out of tube a; and the same operation is repeated, until the carbonate is completely decom- posed. A is then heated to from 176 to 194 F., the wax stopper (or india-rubber cap) opened a little, and suction applied to, the tube d, until the air tastes no longer of carbonic acid. The diminu- tion of weight is ascertained when the apparatus is completely cooled. It will be seen at a glance that a different construction may also be given to the apparatus ; that, for instance, the tube a may be connected, instead of with B, with a chloride of calcium tube, or with a tube filled with pumice stone or asbestos moistened with sulphuric acid ; also, that the substance to be analysed may be put into a small tube, which * Or india-rubber cup, with glass rod. See aa. Fig. 67. Fig. 68. CARBONIC ACID. 267 stands upright at first, or suspended from a thread, but subsequently, after weighing the apparatus, upset- or lowered into the dilute acid in the flask ; also, that the closing of a may be effected by means of an india- rubber connector with compression clamp, &c. Such modifications, if they are judicious, do not alter the accuracy of the results. Fig. 68 shows an apparatus modified in this manner, by Fr. Mohr. The apparatus proposed by Geissler (" Journ. f. prakt. Chemie," 60, 35) is one of the most convenient (see Fig. 69). The apparatus consists of two parts, A B and c. c is ground into the neck of A (a), so as to close air-tight, and yet admit of being readily removed, for the purpose of filling and emptying A. b c is a glass tube, open at both ends, and ground water-tight into c, at the lower end (c); it is kept in the proper position by means of a movable cork, i. The illustration shows the construction of the apparatus in other respects. The cork e must close air-tight, as must the tube d in the cork. The weighed substance to be decomposed is put into A, water added to the extent indicated in the engraving, and the substance shaken towards the side of the flask, c is now filled nearly to the top with dilute nitric acid, with the aid of a pipette, after having previously turned the cork i upwards, without raising b ; the cork is then again turned down, and c inserted into A ; B is filled somewhat more than half with concentrated sulphuric acid, and b closed at the top with a little wax stopper, or a piece of india-rubber tube, with a small glass rod in- serted in it. After weighing the apparatus, the decomposition is effected by raising b a little, and thus causing acid to pass from c into A. The carbonic acid escapes through h into the sulphuric acid, where it is dried ; it then leaves the apparatus through d. After the decomposition has been effected, A is gently heated, the little wax stopper on b opened, and the carbonic acid still remaining in the apparatus sucked out through d, by means of a small india-rubber tube. The apparatus is finally weighed when cold.* ft. Determination of the Acid by expulsion and conversion into Car- bonate of Lime or Carbonate of Baryta. Expel the carbonic acid by a stronger acid, and conduct the expelled acid into a solution of chloride of calcium, or chloride of barium, mixed with ammonia, or into a solution of ammonia, to which chloride of * Several other forms of this apparatus have been proposed by H. Rose, Fritsche, Rogers (see H. Rose's "Manual of Analytical Chemistry," ii. 806) ; Vohl ("Anna!, d. Chem. u. Pharm.," 66, 247); M. Schaffner (" Annal. d. Chem. u. Pbarni.," 82, 335) ; Werther (Modification of Geissler's apparatus "Journ. f. prakt. Chem.," 61, 99) ; J. D. Smith (" G\iem. Graz.," 1855, 201); A.Mayer ("Journ. f. prakt. Chem.," 67, 63); Th. Simmler ("Journ. f. prakt. Chem.," 71, 158) ; Al. Bauer (private communication), and others. 268 CARBONIC ACID. [ 139. calcium, or chloride of barium is afterwards added. Determine the carbonic acid iu the carbonate of lime or baryta formed, as in I., b. The construction of proper apparatus for the expulsion of carbonic acid and its subsequent absorption, offers a wide field to the ingenuity of inventors. However, the apparatus constructed by Fr. Mohr answers the purpose very well (see Fig. 70). Fig. 70. b contains the weighed substance, some water, and a little tincture of litmus ; d, hydrochloric acid. The flask a is filled about | with ammonia quite free from carbonic acid,* the liquid being poured in through the tube c, which contains coarse fragments of glass. The two flasks are united by a connecting tube bent twice at right angles. The limb in a does not reach sufficiently low down to dip into the ammonia. When everything is properly prepared, and the operator has convinced himself that the apparatus is perfectly tight, the clamp which closes the caoutchouc connector at the top of d is opened, so as to allow acid to flow out from d, until the fluid in b looks intensely red. The con- tents of b are then heated to boiling. After this, the source of heat is re- moved to allow b to fill again with air ; the contents of b are again heated to boiling, and the same operation repeated several times. This serves to force every trace of carbonic acid from b into a. It is advisable, in * The ammonia must remain, clear when mixed with chloride of calcium and heated 140.] SILICIC ACID. 269 this operation, to warm the ammonia in a, so as to fill the empty part of the flask with ammoniacal gas. When the apparatus is quite cold, the flask b is removed, and the perforated cork ta.ken out of the tube c. The fragments of glass in the latter are thoroughly rinsed with distilled water boiled free from air, as also the limb of the connecting tube in a, the rinsings of course flowing into the flask a. A sufficient quantity of solution of chloride of calcium is now added to the fluid in a, the mixture heated to boiling, filtered, and the further process con- ducted as in I., b, a, lib. t fr. Mohr obtained yery accurate results by this method. 140. 2. SILICIC ACID. I. Determination. The direct estimation of silicic acid is invariably effected by con- verting the soluble modification of the acid into the insoluble modifica- tion, which is effected by evaporating and heating ; the insoluble modifi- cation is then, after removal of all foreign matter, ignited and weighed. For the guidance of the student I would observe here that, to guard against mistakes, he should always test the purity of the weighed silicic acid. The methods of testing will be found below. If you have free silicic acid in the state of hydrate, in an aqueous or acid solution free from other fixed bodies, simply evaporate the solution in a platinum dish, ignite and weigh the residue. II. Separation of Silicic Add from tlie Bases. a. In all Compounds which are decomposed by Hydrochloric or Nitric Acid. To this class belong the silicates soluble in water, as well as many of the insoluble silicates, as, for instance, nearly all zeolites. The compound under examination is very finely pulverized, the powder dried at a temperature not exceeding 212 F., and put into a platinum or porcelain dish (in the case of silicates whose solution might be at- tended with disengagement of chlorine, platinum cannot be used) ; a little water is then added, and the powder mixed to a uniform paste. Moderately concentrated hydrochloric acid, or, if the substance contains lead or silver, nitric acid, is now added, and the mixture digested at a very gentle heat, with constant stirring, until the substance is com- pletely decomposed, in other terms until the glass rod, which is rounded at the end, encounters no more gritty powder, and the stirring proceeds smoothly without the least grating. The silicates of this class do not all comport themselves in the same manner in this process, but show some differences ; thus most of them form a bulky gelatinous mass, whilst in the case of others the silicic acid separates as a light pulverulent precipitate ; again, many of them are decomposed readily and rapidly, whilst others require protracted digestion. When the decomposition is effected, the mixture is evaporated to dryness on the water- bath, and the residue heated, with frequent stirring, until all the small lumps have crumbled to pieces, and the whole mass is thoroughly dry, and until no more acid fumes escape. It is always the safest way to conduct the operation of drying on the water-bath. 270 SILICIC ACID. [ 140. Ill cases where it appeal's desirable to accelerate the desiccation by the application of a stronger heat, an air-bath may be had recourse to ; which may be constructed in a simple way, by suspending, by wire hooks, the dish containing the substance, in a somewhat larger dish of silver or iron, in a manner to leave everywhere between the two dishes a small space of uniform width. Direct heating over the lamp is not advisable, as in the most strongly heated parts the silicic acid is liable to unite again with the separated bases to compounds which are not decomposed, or only imperfectly, by hydrochloric acid. When the mass is cold, it is brought to a state of semi-fluidity by thoroughly moistening it with hydrochloric acid ; after which it is allowed to stand for half an hour, without heating ; it is then diluted with hot water, stirred, allowed to deposit, and the fluid decanted on to a filter ; the residuary silicic acid is again treated with hot water, the mixture stirred, allowed to deposit, and the fluid once more decanted; after a third repetition of the same operation, the precipitate also is transferred to the filter, thoroughly washed with hot water, well dried, and at last strongly ignited, as directed in 52 or in 53. For the properties of the residue, see 93, 9. The results are accurate. The bases, which are in the filtrate as chlorides, are determined re- spectively by the appropriate methods. Deviations from the instructions here given are likely to entail loss of substance; thus, for instance, if the mass is not thorougJdy dried, a not inconsiderable portion of the silicic acid passes into the solution, whereas, if the instructions are strictly complied with, only traces of the acid are dissolved; in accurate analyses, however, even such minute traces must not be neglected, but should be separated from the bases precipitated from the solution. This separation may be readily efiected by dissolving the precipitated bases, after ignition and weighing, in hydrochloric or sulphuric acid, with the aid of heat ; the minute portion of silicic acid which has passed into the solution, and has been thrown down with the bases, is left undissolved. Again, if the silicic acid is not thorougJdy dried previous to ignition, the aqueous vapor disengaged upon the rapid application of a strong heat may carry away particles of the light and loose silica. Thepurity of the silicic acid* is tested best in the following manner : heat a moderately concentrated solution of pure carbonate of soda to boiling, in a silver or platinum dish, or in a porcelain dish, and add a small quantity of the silicic acid. If it dissolves completely, this is a proof of its purity; but if it leaves a residue, the remainder of the silicic acid must be weighed, and the substance or substances which it contains in admixture determined as directed in b, and the result, of course, calculated upon the whole amount analysed. If you have pure hydrofluoric acid, you may also test the purity of the silicic acid in a very easy manner, by pouring this acid over it, in a platinum dish ; upon the evaporation of the solution, the silicic acid, if pure, will volatilize completely (as fluoride of silicon). If a residue remains, moisten this once more with hydrofluoric acid, add a few drops of sulphuric acid, evaporate, and ignite ; the residue consists of the sulphates of the bases which the silicic acid contained in admixture (Berzelius). * This testing is more especially necessary in cases where the silicic acid has sepa- rated, not in the gelatinous state, but in the pulverulent form. 140.] SILICIC ACID. 271 b. Compounds which are not decomposed by Hydrochloric Acid or Nitric Acid. a. Decomposition and Solution by Fusion with Carbonated Alkali. Reduce the substance under examination to an impalpable powder, by trituration and sifting ( 25) ; transfer to a platinum crucible, and mix with about 4 times the weight of pure anhydrous carbonate of soda or carbonate of soda and potassa, with the aid of a rounded glass rod ; wipe the rod against a small portion of carbonate of soda on a card, and transfer this also from the card to the crucible. Cover the latter well, and heat, according to size, over a gas- or spirit-lamp with double draught, or in a blast gas-lamp ; or insert in a Hessian crucible, compactly filled up with calcined magnesia, and heat in a charcoal fire. Apply at first a moderate heat, to make the mass simply agglutinate ; the carbonic acid will, in that case, escape from the porous mass, with ease and without spurting. Increase the heat afterwards, finally to a very high degree, and terminate the operation only when the mass appears in a state of calm fusion, and gives no more bubbles. The platinum crucible in which the mass is fused must not be too small ; in fact, the mixture should only half fill it. The larger the crucible, the less risk of loss of substance. As it is of importance to watch the progress of the operation, the lid must be easily removable ; a simple concave cover, loosely put on, is therefore preferable to an over- lapping lid. If the process is conducted over the spirit- or simple gas-lamp, a mixture of carbonate of soda and carbonate of potassa is preferable to carbonate of soda, as it fuses much more readily than the latter. In heating over a lamp, the crucible should always be supported on a triangle of platinum wire (see Fig. 57), with the opening just sufficiently wide to allow the crucible to drop into it fully one-third, yet to retain it firmly, even with the wire at an intense red heat. When con- ducting the process over a spirit-lamp with double draught, or over a simple gas-latnp, it is also advisable, towards the end of the operation, "when the heat is to be raised to the highest degree, to put a chimney over the crucible, with the lower border resting on the ends of the iron triangle which supports the platinum triangle ; this chimney should be about 12 or 14 centimetres high, and the upper opening measure about 4 centimetres in diameter. When the fusion is fully effected, the red-hot crucible is removed with pincers, and placed on a cold, thick, clean, iron plate, or marble slab, on which it will rapidly cool ; it is then generally easy to detach the fused cake in one piece. The cake (or, under certain circumstances, the crucible with its contents) is put into a beaker, from 1 to 15 times the quantity of water poured over it, and hydrochloric acid gradually added, or, under certain circumstances, nitric acid ; the beaker is covered with a glass plate, or, which is nmch better, with a large watch-glass or porcelain dish, perfectly clean outside, to prevent the loss of the drops of fluid which the escaping carbonic acid carries along with it ; the drops thus intercepted by the cover are after- wards rinsed into the beaker. The crucible is also rinsed with dilute hydrochloric acid, and the solution obtained added to the fluid in the beaker. The solution is promoted by the application of a gentle heat, which is continued for some time after, to ensure the complete expulsion of the 272 SILICIC ACID. [ 140. carbonic acid ; since otherwise some loss of substance might be incurred, in the subsequent process of evaporation, by spurting caused by the escape of that acid. If in the process of treating the fused mass with hydrochloric acid, a powder subsides (chloride of sodium or chloride of potassium), this is a sign that more water is required. If the decomposition of the mineral has succeeded to the full extent, the hydrochloric acid solution is either perfectly clear, or light flakes of silicic acid only are floating in it. But if a heavy powder subsides, which feels gritty under the glass rod, this consists of undecomposed mineral. The cause of such imperfect decomposition is generally to be ascribed to imperfect pulverization. In such cases the undecomposed portion may be fused once more with carbonated alkali; the better way, however, is to repeat the process with more finely pulverized mineral. The hydrochloric or nitric acid solution obtained is poured, together with the silicic acid floating in it, into a porcelain or, better, into a platinum dish, and treated as directed in 140, II., a. That the fluid may not be too much diluted, the beaker should not be rinsed, or only once, and the few remaining drops of solu- tion dried in it ; the trifling residue thus obtained is treated in the same way as the residue left in the evaporating basin. This is the method most commonly employed to effect the decomposi- tion of silicates insoluble in acids; that it cannot be used to determine alkalies in silicates is self-evident. ft. Decomposition and Solution by means of Hydrofluoric Add. aa. By Hydrated Hydrofluoric Add. The finely- pulverized silicate is mixed, in a platinum dish, with rather concentrated, slightly fuming hydrofluoric acid, the acid being added gradually, and the mixture stirred with a thick platinum wire. The mix- ture, which has the consistence of a thin paste, is digested some time on a water-bath at a gentle heat, and pure hydrated sulphuric acid, diluted with an equal quantity of water, is then added drop by drop, in more than sufficient quantity to convert all the bases present into sulphates. The mixture is now evaporated on the water-bath to dryness, during which operation fluoride of silicon gas and hydrofluoric acid gas are con- tinually volatilizing ; then it is finally exposed to a stronger heat, over the lamp, with proper caution, until the excess of sulphuric acid is com- pletely expelled. The mass, when cold, is thoroughly moistened with concentrated hydrochloric acid, and allowed to stand at rest for one hour ; water is then added, and a gentle heat applied. If the decomposition has fully succeeded, the whole must dissolve to a clear fluid. If an undissolved residue is left, the mixture is heated for some time on the water bath, then allowed to deposit, the clear supernatant fluid decanted off as far as practicable, the residue dried, and then treated again with hydrofluoric acid and sulphuric acid, and, lastly, with hydrochloric acid, which will now effect complete solution, provided the analysed substance was very finely pulverized, and free from baryta, strontia (and lead). The solution is added to the first. The bases in the solution (which contains them as sulphates, and contains also free hydrochloric acid), are determined by the methods which will be found in Section V. This method, which is certainly one of the best to effect the decompo- sition of silicates, has Berzelius for its author. It has been but little 140.] SILICIC ACID. 273 used hitherto, because we did not know how to prepare hydrofluoric acid, except with the aid of a distilling apparatus of platinum, or, at least with a platinum head ; nor to keep it, except in platinum vessels. This difficulty, however, would appear to be overcome now, since Stddeler ("Annal. d. Chern. und Pharm.," 87, 137) has made the discovery that gutta percha and vulcanized india-rubber resist the action of hydrofluoric acid. Stiideler prepares the acid in a leaden retort having the shape of a digesting glass with the neck cut off. The retort has about 5 baches inner diameter; the width of the very short neck is If inches. A close-fittiug wide leaden pipe, 4 inches long, is put into the mouth of the neck, which is turned perfectly even and smooth inside ; the upper end is a little contracted, so that it may be closed with a common cork, which bears a double-limbed thin leaden pipe. The length of the longer limb is 6 inches ; this limb is connected with a tube of stout vulcanized india-rubber, which opens into the gutta-percha vessel intended to re- ceive the hydrofluoric acid, but barely dips into the water in the receiver, by which precaution the receding of the acid is guarded against. Care must be taken to keep the receiver properly cooled. The gutta-percha vessels in which the acid is kept have the form of common bottles, and are closed with gutta-percha stoppers.* The execution of the method requires the greatest possible care, both the liquid and the gaseous hydrofluoric acid being most dangerous substances. The treatment of the silicate with the acid and the evapo- ration must be conducted in the open air, otherwise the windows and ajl glass vessels and glass apparatus will be greatly injured. As the silicic acid is in this method simply inferred from the loss, a combination of the two methods, a and /3, aa is often resorted to. lib. By Hydrofluoric Acid Gas. Instead of the hydrofluoric acid dissolved in water, the gaseous acid also may be used to effect the decomposition of silicates. Brunner (" Pogg. Anna!.," 44, 134) is the author of this method, which is very often em- ployed. The process is as follows: Put from 1 to 2 grammes of the silicate, very finely pulverized, in the thinnest possible layer, into a shallow platinum dish, and moisten the powder with water or with' dilute sulphuric acid ; place the dish, supported on a leaden tripod or leaden ring, in the centre of a leaden box, which may have a diameter of 6 inches and a height of 6 inches, and on the bottom of which you have just before spread a layer of about half an inch of powdered fluor-spar, made into a thick paste with concentrated sulphuric acid; in this latter operation, be cautious to avoid the escaping vapors ; the mixing of the powdered fluor-spar with the sulphuric acid is effected with a long glass rod, or, better still, with a long leaden rod. As soon as you have placed the small dish into the box, with the aid of a pair of pincers, put on the tightly fitting leaden cover, lute the joinings with gypsum paste, and put the box in a warm place for from 6 to 8 days. If you wish to accelerate the process, you must not lute the joinings quite air-tight, and must heat the apparatus in the open air by means of a small spirit- lamp ; in this manner you may succeed in a few hours to effect the decomposition of from 1 to 2 grammes of the powdered silicate, provided it is spread in a very thin layer, or stirred from time to time, which latter operation, however, requires caution. * These bottles may be procured at the Gutta-percha Works, City Koad. II. T 274 SILICIC ACID. % [ 140. If the decomposition has succeeded well, the residue in the platinum dish consists of metallic silico-fluorides and (if you have used sulphuric acid . to moisten the powder) sulphates. Put the shallow dish now into a larger platinum dish, add, drop by drop, pure sulphuric acid, in somewhat more than sufficient quantity to effect the conversion of the bases into sulphates ; evaporate in the air-bath, expel finally the excess of hydrated sulphuric acid over the lamp, and treat the residue with hydrochloric acid and water in the manner directed in /3, aa. The decomposition can only be considered complete if the residue is entirely dissolved. y. Decomposition and Solution of Silicates by fusion with Hydrate of Baryta or Carbonate of Baryta. The fusion of silicates with carbonate of baryta requires a very high degree of heat, attainable only by means of a Sefstrom furnace, or $.Griffiris gas-furnace or a blast gas-lamp, or a Deville turpentine lamp, &c.; as the highest temperature attainable by means of a wind furnace fails to fuse carbonate of baryta, and it is only in a state of fusion that this reagent effects complete decomposition of silicates. But then, on the other hand, the action of carbonate of baryta in a state of fusion is so energetic, that even the most refractory siliceous minerals are readily and completely decomposed by it. The proportion is from 4 to 6 parts of carbonate of baryta to 1 part of the mineral. The fusion is effected in a platinum crucible, which, if a Sefstrom furnace is used, is inserted in another crucible of refractory fire-clay, filled with magnesia. The crucible is left in the fire a quarter of an hour at least. With more readily decomposable minerals, the object in view may be attained more easily with hydrate of baryta freed from its water of crystallization. From 4 to 5 parts of the hydrate are intimately mixed with 1 part of the mineral ; it is advisable to cover the mixture with a layer of carbonate of baryta. The fusion may be effected over a com- mon gas- or Berzelius spirit-lamp ; silver crucibles are preferable to platinum, as the latter are slightly affected by the operation. The mixture fuses completely, or, at least, its particles agglutinate into a semi-fused mass. When the operation is terminated no matter whether carbonate or hydrate of baryta has been employed the crucible is allowed to cool, care- fully cleaned outside, and put with its contents into a beaker, where it is then covered with from 10 to 15 parts of water ; hydrochloric or nitric acid is added, and the rest of the operation conducted as in b, a. Care must be taken, however, not to add too much hydrochloric acid at once, as the chloride of barium formed is difficultly soluble in that acid, and would consequently tend to impede further solution, by forming a kind of insoluble protecting crust round the still undissolved portion. In the solution filtered from the silicic acid, the bases are determined by the methods which will be found in Section V. The purity of the silicic acid obtained must be tested as directed in a, before the operation can be looked upon as successful. These methods, which were formerly often employed to determine the alkalies in silicates, have been in a measure superseded by /3, bb (decomposition by hydrofluoric acid gas). Deville ('' Ann. de Chim. et de Phys.," 3 Ser., 38, 5) has lately called attention to the fact that the quantity of carbonate of baryta usually em- ployed to effect the decomposition of silicates (from 4 to 6 parts) is much larger than required. He states that 1 part of orthoclaoe fuses. at a moderate red heat, with as little as 0'8 parts of carbonate of baryta 141.] HYDROCHLORIC ACID. 275; to a vitreous transparent mass, decomposable by acids. He adds that, if the carbonate is used in larger proportions, an appreciable amount of potassa volatilizes, expelled by the agency of caustic baryta formed in the process. Smith (" Journ. f. prakt. Chem.," 60, 246)* recommends to fuse 1 part of the silicate with from 3 to 4 parts of carbonate of baryta and 2 parts of chloride of barium. 3. Decomposition and /Solution of Silicates by fusion with Lime and Lime Salts. Deville (" Ann. de Chim. et de Phys.," 3 Se~r., 38, 5) recommends also to fuse 1 part of the powdered silicate with from 0-3 to 0'8 parts of carbonate of lime. I have tried this process, but have not found it answer in the case of many silicates. L. Smith (" Journ. f. prakt. Chern.," 60, 246)t recommends to fuse 1 part of the powdered silicate with from 5 to 6 parts of carbonate of lime, and from 0-5 to 0'7 of chloride of ammonium, for 30 or 40 forty minutes, at a bright red heat ; boil the fused mass for 2 or 3 hours with water, taking care to replace the loss from evaporation ; fuse the residue once more with half its weight of chloride of ammonium, and boil the fused mass again with water. He states that, if no boracic acid is present, the whole of the alkalies will be found in the aqueous solution. J. Tipp (" Vierteljahrsschrift f. prakt. Pharm.," IV., 68) confirms this statement. SECOND GROUP. HYDROCHLORIC ACID HYDROBROMIC ACID HYDRIODIC ACID HY- DROCYANIC ACID HYDROSULPHURIC ACID. 141. 1. HYDROCHLORIC ACID. I. Determination. Hydrochloric acid may be determined very accurately in the gravi- metrical, as well as in the volumetrical way. J a. Gravimetrical Method. Determination of Silver as Chloride. Solution of nitrate of silver, mixed with some nitric acid, is added in excess to the solution under examination, the precipitated chloride is made to subside by application of heat and shaking, washed by decan- tation, dried and ignited. The details of the process have been given in 115, 1, a, a. Care must be taken not to heat the solution mixed with nitric acid, before the solution of nitrate of silver has been added in excess. As soon as the latter is present in excess, the chloride of silver separates immediately and completely upon shaking the vessel, and the supernatant fluid becomes perfectly clear after standing a short time in a warm place. The determination of hydrochloric acid by means of silver is therefore more readily effected than that of silver by means of hydro- chloric acid. In the case of smaller quantities of chloride of silver, the precipitate is often collected on a filter; see 115, 1, a, ft. Or the two methods may be combined in this way that the chief portion of the precipitate is washed by decantation, dried in the porcelain crucible, and ignited, the decanted fluid being afterwards passed through a filter, * Sillimari's "American Journal," 1853, vol. xvi. page 53. + Ibid. J For the acidimetric estimation of free hydrochloric acid, see 215. T2 276 HYDROCHLORIC ACID. [ 141. to make quite sure that not a particle of chloride of silver has been lost. The filter is, after drying, incinerated in a platinum wire over the in- verted cover of the porcelain crucible, the ashes are treated with a few drops of nitric acid, some hydrochloric acid is added, the mixture evaporated to dryness, the residue gently ignited, and the lid replaced in the proper position on the crucible in which the chloride has been heated to incipient fusion ; a gentle heat is then once more applied, after which the crucible is allowed to cool under the desiccator, and then weighed. b. Volumetrical Method of estimating Hydrochloric Acid. a. By Solution of Nitrate of Silver. In 1 15, 5, we have seen how the silver in a fluid may be estimated by adding a solution of chloride of sodium of known strength until no further precipitation ensues ; in the same way we may determine also, by means of a solution of silver of known strength, the amount of hydrochloric acid in a fluid, or of chlorine in combination with a metal. Pelouze has used this method for the determination of several equiva- lent numbers. Levol has proposed a modification which serves to in- dicate more readily and accurately the exact point of complete precipi- tation. This modification consists in the addition of O'l volume of a saturated solution of phosphate of soda to the neutral fluid. When the whole of the chlorine has been precipitated by the silver, the addition of another drop of the solution of silver produces a yellow precipitate which does not disappear upon shaking the vessel (" Journ. f. prakt. Chein.," 60, 384). Fr. Mohr has since replaced, with the most complete success, the phosphate of soda by chromate of potassa. This convenient and accurate method requires two solutions of known strength, viz., one of chloride of sodium, and another of nitrate of silver, free from excess of acid. The best way is to use the decimal standard solutions mentioned in 115, b, 5, d, which contain in 1 litre of fluid, respectively, 5'846 grm. of chloride of sodium, and 10-797 grm. of silver. As the silver solution must be free from acid, it is advisable to prepare it by dissolving 10'797 grm. of pure silver in dilute nitric acid, in a flask placed in a slanting position ; evaporating the solution, in a large porcelain dish, cautiously, to dryness (until no more acid fumes escape), dissolving the residue in water, transferring the solution to the litre-flask, diluting to the mark, and snaking. Before the standard solutions of chloride of sodium and nitrate of silver can be employed, their strength must be tested. This is done by mixing 20 c.c. of the one with 20 c.c. of the other, shaking the mix ture, applying heat, letting the precipitate subside, decanting, and adding to one portion of the clear fluid a drop of solution of nitrate of silver, to the other a drop of solution of chloride of sodium. If the solutions are of the exact strength indicated, and the measuring vessels quite accurate, both portions of the fluid must remain clear. It is now, in the first place, necessary to study the exact point of the completion of the chromate of potassa reaction. To this end, about 10 cub. cent, of fluid are allowed to flow out from the burette containing the standard solution of chloride of sodium; the height of the fluid is read off with the greatest accuracy, 4 or 5 drops of a cold saturated solution of pure neutral chromate of potassa are added, and then to the bright yellow fluid, from another burette, drop by drop, standard solution of $ 141.] HYDROCHLORIC ACID. 277 nitrate of silver. As each, drop falls into the fluid, it produces a red spot, which disappears again on stirring, owing to the instant decompo- sition of the newly-formed chromate of silver with the chloride of sodium. At last, however, the red coloration remains, which is a sign that the whole of the chlorine present has combined with the silver, and that a little chromate of silver has been permanently formed. On reading off now, it is constantly found that there has been consumed in the process almost exactly O'l cub. centimet. more of the silver solution than of the chloride of sodium solution. This trifling excess arises from the fact that it requires Ol of solution of nitrate of silver to produce a sufficient quantity of chromate of silver to impart a distinct red coloration to the fluid. If the red coloration is too strongly marked, solution of chloride of sodium may be added, drop by drop, until it has disappeared again; addition of O'l cub. cent, of the silver solution will then reproduce the red tint. As the two standard solutions are of equal value, the sup- plementary quantity of chloride of sodium solution added need simply be subtracted from the silver solution. With a correct appreciation of the transition point from yellow to red, it is an easy task to estimate with great accuracy hydrochloric acid, or chlorine in metallic chlorides soluble in water. It must be borne in mind, however, that the fluid must be neutral or very slightly alkaline, but on no account acid, as free acids dissolve chromate of silver. The solution of the weighed sample under examination must, therefore, if required, be made quite neutral or veiy slightly alkaline, by addition of nitric acid or of carbonate of soda. 4 or, 5 drops of solution of neutral chromate of potassa ai - e then added to the fluid, and afterwards solution of nitrate of silver, drop by drop, from the burette, until the exact point is reached at which the red color becomes permanent. O'l cub. cent, is deducted from the number of cubic centimetres of silver solution used in the process ; the remainder shows the quantity of the hydrochloric acid, or of the chlorine in the examined chloride ; since 1000 cub. cent, of the solution of nitrate of silver corresponds respectively to 3*646 H 01, 3-546 chlorine, 5-846 Na 01, &c., i.e. to the decimal equivalent numbers of the substances sought. Should a loss have occurred in the evaporation of the silver solution, the correct strength must be determined again by making it act re- peatedly upon 20 cub. cent, of the standard solution of chloride of sodium. The proportion found forms the basis of the calculations, in the determinations of chlorine by the solution. In such cases, however, the subtraction of O'l c.c. of silver solution is omitted in the first, as well as in all the subsequent experiments. Fr. Mohr obtained very satisfactory results by this method, and I can say the same of the experiments made with it in my own laboratory. /3. By Solution of Nitrate of Silver and Iodide of Starch (Pisanfs method " Annal. d. Mines," X. 83. Liebig and Kopp's " Jahresbericht" 1856, 751). Add to the solution of the chloride, acidified with nitric acid, a slight excess of solution of nitrate of silver of known strength, warm, and filter. Determine the excess of silver in the filtrate by means of solution of iodide of starch (see 163, Separation of Silver from Lead), and deduct this from the amount of silver solution used. The difference shows the quantity of silver which has combined with the chlorine ; calculate from this the amount of the latter. Results satisfactory. 278 .HYDROCHLORIC ACID. [ 141. y. With Solution of Nitrate of Oxide of Mercury (Liebig's method "Annal. d. Chem. u. Pharm.," 85, 297); recommended more par- ticularly for the determination of chlorine in the chlorides contained in the urine. aa. Principle of the method. Nitrate of oxide of mercury immedi- ately produces in a solution of urea a thick white precipitate ; solu- tion of chloride of mercury produces no such pi*ecipitate. When. a solution of nitrate of oxide of mercury is mixed with the chloride of an alkali, there is formed chloride of mercury and nitrate of the alkali. If, therefore, a solution of urea is mixed with chloride of sodium, and a dilute solution of nitrate of oxide of mercury is added, drop by drop, the fluid will show in the points of contact a white turbidity, which, however, will immediately disappear upon shaking, so long as the nitrate of oxide of mercury continues to decompose and transpose with the chloride of sodium in the manner just stated ; but the moment this double decomposition is complete, an additional drop of the solution of the salt of mercury will produce a permanent white turbidity. Accordingly, if we know the measure and strength of the solution of the salt of mercury required to attain this point, we know also the amount of chlorine in the solution ; since 1 equivalent of mercury in the mercurial solution corresponds to 1 equivalent of chlorine. bb. Preparation of the solution of nitrate of oxide of mercury. As this solution must be perfectly free from other metals, it is advisable to prepare it with oxid| of mercury precipitated from solution of crystallized chloride of mercury by solution of soda, and thoroughly washed by dissolving 10*8 grm. of the dry oxide in nitric acid, evaporating the solution to the consistence of syrup, and diluting with water to the volume of 550 cubic centimetres. Or the solution may be made by dissolving repeatedly re- crystallized nitrate of suboxide of mercury in water, with addi- tion of nitric acid, heating to boiling, adding strong nitric acid until no more red fumes escape, evaporating to the consistence of syrup, and diluting with a proper quantity of water to give a solution of tolerably correct concentration. cc. Determination of the strength oftJie solution. This is effected with the aid of a solution of chloride of sodium of known strength, which Liebig prepares by mixing 20 cubic centimetres of a satu- rated* solution of pure rock salt or chemically pure chloride of sodium, with 2984 cubic centimetres of water. Every cubic centimetre of this solution contains 20 milligrammes of chloride of sodium. Of this solution of chloride of sodium measure 10 cubic cen- timetres into a small beaker, and add 3 c.c. of a solution of urea containing in 100 c.c. 4 grammes of urea. Let the solution of mercury, of which you wish to ascertain the strength, drop into this mixture, from a burette, or from a pipette provided with a caoutchouc connector and a clamp, until a perceptible precipitate forms, which on shaking fails to re- dissolve, t * Saturated at the common temperature. ( A mere opalescence of the fluid is disregarded, as this proceeds simply from a trace of foreign metals, which is readily seen from the circumstance that a further addition of the mercurial solution does not increase the turbidity. , 141.] CHLORINE. 279 del. When you have in this way ascertained how many c.c. of the mercurial solution correspond to the 10 c.c. of the solution of common salt = 0'2 grm. of chloride of sodium, you may use the mercurial solution without further preparation, if you do not mind the trouble of a little calculation. But if you wish to avoid this, you must previously dilute the mercurial solution in a manner that every cubic centimetre corresponds to an integral number of milligrammes of chloride of sodium or chlorine. Liebig dilutes it to the extent that 1 cubic centimetre corresponds to O'OIO grm. of chloride of sodium. ee. If the test fluid is intended to examine solutions containing a large amount of foreign salts, or an excess of urea, the 10 c.c. of the chloride of sodium solution must be mixed with 5 c.c. of a cold saturated solution of sulphate of soda,* in addition to the 3 c.c. of solution of urea, before the mercurial solution is added. The results are accurate. If you have a decimal standard solution of chloride of sodium, containing 5'846 grm. in the litre, you may, of course, also deter- mine the strength of the mercurial solution by means of this. JFr. Mohr uses ferricyanide of potassium instead of urea. This reagent requires, however, still greater purity of the mercurial solution than is the case where urea is used ; otherwise permanent precipitates of ferricyanides are formed from the beginning, which of course obscure the final reaction. Of these volumetrical methods of estimating chlorine, the first deserves the preference in all ordinary cases. It cannot be em- ployed, however, in analyses of urine, as compounds of oxide of silver with coloring matters, &c., precipitate along with the chloride of silver (C. Neubauer). Pisanis method (b, /3) is especially suited for the estimation of very minute quantities of chlorine. II. Separation of Chlorine from, the Metals. a. In Soluble Chlorides. The same method as in I., a. The metals in the filtrate are separated from the excess of the salt of silver by the methods which will be found in Section V. Bichloride of tin, cldoride of mercury, the chlorides of antimony, and the green protochloride of chromium, form exceptions from the rule, and are determined respectively by the following methods : a. From solution of bkldorlde of tin, nitrate of silver would precipitate, besides chloride of silver, a mixture of binoxide of tin and oxide of silver. To precipitate the tin, therefore, the solution is mixed with a concentrated solution of sulphate of soda, or nitrate of ammonia, allowed to deposit, the fluid decanted, and filtered (compare 126, b, 1, b), and the chlorine in the filtrate precipitated with solution of silver. Lowenthal, the inventor of this method, has proved its accuracy (" Journ. f. prakt Chern.," 56, 371). * The reason of this addition is, that the nitrate of oxide of mercury and urea is more readily soluble in pure water than in saline solutions ; to attain accurate results, therefore, it is necessary that the solvent power of the fluids should be as nearly as possible the same in the preliminary determination of the strength of the mercurial solution as hi the subsequent analytical process. 280 CHLORINE. [ 141. /3. When a solution of chloride of mercury is precipitated with solution of nitrate of silver, the chloride of silver thrown down contains an admixture of mercury. The mercury is, therefore, first precipitated by sulphuretted hydrogen, which must be added in sufficient excess, and the chlorine in the filtrate determined as directed in 165. y. The chlorides of antimony are also decomposed in the manner described in (3. The % separation of basic salt upon the addition of water may be avoided by addition of tartaric acid. & Solution of silver fails to precipitate the whole of the chlorine from solution of the green protochloride of chromium (Peligot). The chromium is, therefore, first precipitated with ammonia, the fluid filtered, and the chlorine in the filtrate precipitated as directed in L, a. b. In Insoluble Chlorides. a. Chlorides soluble in Nitric Acid. Dissolve the chloride in nitric acid, without applying heat, and proceed as directed in I., a. /3. Chlorides insoluble in nitric acid (chloride of lead, chloride of silver, eubchloride of mercury). aa. Chloride of lead is decomposed by digestion with alkaline bicarbonates and water. The process is exactly the same as for the decomposition of sulphate of lead ( 132, 11, b, /3). bb. Chloride of silver is ignited in a porcelain crucible, with 3 parts of carbonate of soda and potassa, until the mass commences to agglutinate. Upon treating the mass with water, the metallic silver is left undissolved ; the solution contains the alkaline chloride, which is then treated as directed in II., a. Chloride of silver may also be readily decomposed by digestion with pure zinc, and dilute sulphuric acid. The separated metallic silver may be weighed in that state ; it must afterwards be ascertained, however, whether it dissolves in nitric acid to a clear fluid. The chlorine is determined in the solution of chloride of zinc obtained, as in II., a. cc. Subchloride of mercury is decomposed by digestion with solution of soda or potassa. The hydrochloric acid in the filtrate is deter- mined as in II., a. The suboxide of mercury is dissolved in nitro-hydrochloric acid, and the mercury determined as directed in 118. c. The soluble chlorides of the metals of the fourth, ffth, and sixth groups may all be decomposed also by sulphuretted hydrogen, or, as the case may be, sulphide of ammonium. The hydrochloric acid in the filtrate is determined as directed in 1 69. d. In many metallic chlorides, for instance, in those of the first and second groups, the chlorine may be determined also by evaporating with sulphuric acid, converting the base thus into a sulphate, which is then ignited and weighed ; the chlorine being calculated from the loss. This method is not applicable in the case of chloride of silver and chloride of lead, which are only imperfectly and with difficulty decomposed by sul- phuric acid ; nor in the case of chloride of mercury and bichloride of tin, which sulphuric acid fails altogether to decompose, or decomposes only to a barely perceptible extent. 11:2.] CHLORINE. 281 Supplement. Determination of Chlorine in tlie Free State. 142. Chlorine in the free state may be determined both in the volumetrical and in the gravimetrical way. The volumetrical methods, however, deserve the preference in most cases. They are very numerous. The following are the best.* 1. Volumetrical Metftods. a. With Iodide of Potassium and Iodine (Sunsen's method). Bring the chlorine, in the gaseous form or in aqueous solution, into contact with an excess of solution of iodide of potassium in water (compare 130, d, /3). Each equivalent of chlorine liberates 1 equiva- lent of iodine. By determining the liberated iodine, by the method given in 146, you will accordingly learn with the greatest accuracy the quantity of the chlorine. b. With Arsenite of Soda and Iodine (Fr. Mohrs method, slightly modified). The process requires, aa. A solution of iodine in iodide of potassium of most accu- rately known strength. The same solution is usually em- ployed, which serves for the estimation of iodine, &c., by Eunserus method (see 146). It contains, in the cubic centimetre, about 0-005 grm.t of iodine, which we will here assume to be the fixed standard of it. This, calculated for chlorine, corre- sponds to 0-00139 grm. of chlorine. bb. A solution of arsenite of soda. This is prepared by boiling 5 grammes of pure arsenious acid with 10 grammes of bicarbonate of soda in water, until complete sohition is effected. The solu- tion is then diluted with water to the volume of a litre. This solution has at first a fixed strength ; but there is no reliance to be placed upon its retaining this strength for any length of time, as it would appear that arsenite of soda will, under certain circumstances not yet quite settled, attract oxygen from the atmosphere, with greater or less rapidity, and suffer conversion, to a greater or less extent, into arsenate of soda. J The relative proportion between the solution of arsenite of soda and the iodine solution must, therefore, be determined before every fresh series of experiments, the known strength of the iodine solution being always taken for the basis. To this end, 10 cubic centimetres of the arsenical solution are measured off, slightly diluted, 10 c.c. of a cold saturated solution of bicarbonate of soda added, then a little starch paste, and the iodine solution drop by drop, until a permanent blue coloration * Compare article " Chlorimetry" in the Special Part, 224. f- Mohr recommends the use of a solution of iodine containing only ,qnr equivalent = 1'269 grm. in the litre. This does not appear to me very practical, as it necessitates a repeated filling of the burette in almost every experiment. It would appear also, from Mohr's own showing, that he himself usually employs a more concentrated solution. Fresenius, "Annal. d. Chem. u. Pharm.," 93, 384. Fr. Mohr, ibid., 94, 222. W. Mayer, ibid. 101, 266. 282 .CHLORINE. [ 142. is produced. Suppose 26 c.c. of iodine solution have been used to 10 c.c. of the arsenite of soda solution, to produce this result. Now, if it is wished to determine by this method the quantity of chlorine in a solution, a definite amount, say 30 c.c., of the arsenite of soda solution is measured off, about an equal amount of a cold saturated solution of bicarbonate of soda added, then a certain mea- sured or weighed quantity, say 20 grammes, of the chlorine water. (The solution of the arsenite of soda must of course be in excess ; whether this is the case, is ascertained by letting a drop of fluid fall upon a slip of iodide of potassium and starch paper,* which must not be tinged blue by it. Should a blue tint be imparted to the paper, an additional mea- sured quantity of the arsenite of soda solution must be added.) The fluid is now mixed with some starch paste, and iodine solution added, until a permanent blue coloration is produced. Suppose there has been consumed in this operation 15 c.c. of iodine solution, it will at once be seen that the difference between the quantity of iodine solution which would have been required for the arsenite of soda solution used (in the case before us, 78 c.c., since 10 : 26:: 30 : 78), and the quantity actually used after the addition of the chlorine water (in the present case, accordingly, 78-15 = 63 cubic centimetres), gives the measure for the quantity of chlorine contained in the chlorine water, 1 equivalent of iodine = 126-88, corresponding of course to 1 equivalent of chlorine = 35 '46. Now, in the case before us, the quantity of iodine solution saved, viz. 68 cubic centimetres, contains 63 x 0-005 = 0-315 grm. of iodine, which, as 0-005 grm. of iodine corre- sponds to 0-00139 grm. of chlorine, corresponds to 63x0-00139 = 0-08757 grm. of chlorine. As this quantity was contained in 20 grammes of the chlorine water, 100 grammes of the latter contain 0-43785 grins, of chlorine. In cases where the chlorine to be estimated is evolved as gas, as in the analysis of chromic acid ( 130, d, /3), or of peroxides, Fr. Mohr uses the absorption apparatus shown in Fig. 71. The large flask should hold about 1 litre ; the wide open tube, fixed by the narrow lower end in the perforated cork of the large flask, is filled with fragments of glass. An excess of arsenite of soda solution is poured into the flask, and a sufficient quantity of solution of carbonate of soda added, through the tube filled with fragments of glass. The small flask serves as evolution flask ; in the analysis of chromates, for instance, the chromate is boiled in it with strong hydrochloric acid. When the gas-conducting tube has become hot in its entire length, and the contents of the large flask begin to effervesce strongly (a sign that hydrochloric gas passes over), and the vapors are absorbed with crackling noise, the little caoutchouc connector is closed with the clamp, the lamp removed immediately after, and the tube disconnected which leads from the small flask to the caoutchouc connector. The fragments of glass are then thoroughly washed, the rinsings running, of course, into the flask, which is allowed to stand with occasional moderate shaking, until it is quite cold. The tube dipping in the fluid is now also taken away and rinsed, the * This is prepared by mixing 3 grms. of pure potato starch in 250 cubic centimetres of cold water, boiling with stirring, adding a solution of 1 grm. of iodide of potassium and 1 grm. of crystallized carbonate of soda, diluting the mixture to about 500 cubic centi- metres, soaking fine white unsized paper in the fluid, and drying. 142.] CHLORINE. 283 rinsings being added to the contents of the large flask. Some starch paste is now added, and then iodine solution until a permanent blue coloration is produced. The final reaction can be looked upon as con- clusive only if the coloration does not disappear again upon addition of solution of carbonate, or, better still, bicarbonate of soda. On discon- necting the apparatus, neither the large nor the small flask must emit the odor of chlorine ; otherwise the experiment is a failure. To afford Fig. 71. some indication of the quantities to be used, I may remark that, in the analysis of bichromate of potassa, for instance, 0-2 0-5 grm. of that salt may be taken, to 40 100 c.c. of arsenite of soda solution in the receiver. Note to a and J. Upon an attentive consideration and comparison of the two preceding methods, a and b, it will be seen that in the former the quantity of iodine is to be determined which has been liberated by chlorine ; whilst in the latter, on the contrary, we have to deal, not with the arsenious acid which has been oxidized, but with the excess of the acid which has not been oxidized. Now, although this is of no great consequence in cases where the amount of chlorine is comparatively large, it is of very considerable importance in cases where the amount of chlorine is only small, more particularly where it unexpectedly turns out to be so, and where, accordingly, a pretty large quantity of arsenate of soda solution has been employed in the analytical process. For, in such cases, it may happen that the small difference which lies within the limits of the 284 CHLORINE. [ 142. errors of observation, and which, under the circumstances, on account of the indefinite and uncertain quantity of carbonate of soda added, is likely to rise to as high as 0-5 c.c., amounting to r V ^, and even more of the difference between the quantities of the iodine solution respec- tively consumed in the experiments, befoi-e and after addition of the chlorine water ; which may lead to very serious errors in the results, to the extent, indeed, of 10 or 20 per cent., and even more. For this reason Bunsens method (a) alone deserves to be recommended for the estimation of smaller quantities of chlorine. c. With Solution of Protoxide of Iron and Permanganate of Potassa. The chlorine solution is mixed with an excess of solution of proto- chloi-ide of iron, or sulphate of protoxide of iron and ammonia of known strength, in a stoppered flask ; the mixture is allowed to stand for some time, and the iron, still left in the state of protochloride or protoxide, determined by solution of permanganate of potassa ( 112). It must be borne in mind, in the calculation, that 2 eq. of protochlo- ride of iron are converted into sesquichloride by 1 eq. of chlorine. This method is suited, indeed, for the estimation of chlorine in aqueous solu- tion ; but it is much less adapted to effect the determination of chlorine when evolved in gaseous form, as the gas is absorbed with comparative slowness by the protochloride of iron solution. 2. Gravimetrical Metliod. The fluid under examination, which must be free from sulphuric acid, say, for instance, 30 grammes of chlorine water is mixed in a stoppered bottle, with an excess, say 0'5 grm., of hyposulphite of soda, the stopper inserted, and the bottle kept for a short time in a warm place ; after which the odor of chlorine is found to have gone off. The mixture is then heated to boiling with some hydrochloric acid in excess, to destroy the excess of hyposulphite of soda, filtered, and the sulphuric acid in the filtrate determined by baryta ( 132). 1 equivalent of sulphuric acid corresponds to 2 equivalents of chlorine ( Wicke, " Annal. d. Chein. u. Pharm.," 99, 99). In fluids containing, besides free Marine, also hydrochloric acid, or a metallic cldoride, the chlorine existing in a state of combination may be determined, in presence of the free chlorine, in the following way : a. A weighed portion of the fluid is mixed with ammonia in excess ;* nitrogen escapes, and the solution contains the whole of the free chlorine as chloride of ammonium (3 Cl + 4 N H 3 = N + 3 [N H 4 Cl]). By pre- cipitating now with solution of silver, we learn the total amount of the chlorine. The quantity of the free chlorine is then determined in another weighed portion, by means of iodide of potassium, or by some other method ; the difference gives the amount of chlorine which the analysed fluid contained in a state of combination. b. A weighed portion of the fluid is mixed with solution of sulphu- rous acid in excess, the mixture acidified with nitric acid, and the whole of the chlorine precipitated as chloride of silver. The further opera- tion is conducted as in a. Having thus seen in how simple a manner the quantity of free chlo- rine may be determined by Bunsens method, and for larger amounts * If chlorine water is mixed at once with solution of nitrate of silver, |ths only of the chlorine are obtained as chloride of silver : 6 Cl + 6 Ag = 5 Ag Cl + Ag 0, Cl O s (H. Rose; Wdtzien, "Annal. d. Chem. u. Pharm.," 91, 45). 143.] HYDROBROMIC ACID. 285 also by Molar's method, it will be readily understood that all oxides and peroxides which evolve chlorine when heated with hydrochloric acid, may be analysed by heating them with concentrated hydrochloric acid, and determining the amount of chlorine evolved. For the modus operandi compare 130, d, /3, and 142, 6. 2. HYDBOBROMIC ACID. I. Determination. -,.. a. Free hydrobromic acid is precipitated from its solution with nitrate of silver, and the further process conducted as in the case of chlorine ( 141). For the properties of bromide of silver, see 94, 2. The re- sults are perfectly accurate. b. Heine s coloriinetrical method* The bromine is liberated by means of chlorine, and received in ether ; the solution is compared, with respect to color, with an ethereal solution of bromine of known strength, and the quantity of bromine contained in it thus ascertained. FeJding ("Journ. f. prakt. Chem.," 45, 269) obtained satisfactory results by this method. It will at once be seen that the amount of bromine con- tained in the fluid to be analysed must be known in some measure, before this method can be resorted to. As the mother liquor examined by Fehling could contain at the most 0'02 grm. of bromine, he prepared ten different test fluids, by adding to ten several portions of 60 grammes each of a saturated solution of common salt increasing quantities of bro- mide of potassium (containing respectively from 0'002 grm. to 0'020 grm. of bromine). He added an equal volume of ether to the test fluids, and then chlorine water, until there was no further change observed in the color of the ether. It being of the highest importance to hit this exact point, F elding pi*epared three samples of each test fluid, and then chose the darkest of them for the comparison. 60 grammes are now takent of the mother liquor to be examined, the same volume of ether added as was added to the test fluids, and then chlorine water. Every experiment is repeated several times. Direct solar light must be avoided, and the operation conducted with proper expedition. c. Figuiers colorimetrical method (" Aunal. de Chim. et de Phys.," 33, 303, and "Journ. f. prakt. Chem.," 54, 293), proposed as a useful method to effect the determination of bromine in mother liquors, &c. This method is based upon the circumstance that 1 equivalent of chlorine (added in the form of chlorine water), liberates from a solution of a metallic bromide 1 equivalent of bromine, and that bromine imparts a yellow color to an aqueous solution, and escapes readily upon boiling, the yellow tint of the solution disappearing again with the escape of the bromine. To carry this method into effect, the strength of the chlorine water is determined at the moment of its application, by making it act upon a solution of bromide of sodium of known strength, acidified with a few drops of hydrochloric acid (or by one of the methods given in 142), and then applying it to the mother liquor. The latter is heated in a flask * "Journ. f. prakt. Chem.," 36, 184, proposed as a useful method to effect the determination of bromine in mother liquors. t The best way is to take them by measure. 286 BROMINE. [ 144. nearly to ebullition ; chlorine water is then added from a burette covered with black paper, and the mixture heated for about 3 minutes, where- upon the yellow tint imparted to the fluid by the addition of the chlorine water will disappear again ; the mixture is now allowed to cool for 2 minutes, after which some more chlorine water is dropped into it, heat again applied, and the same process repeated until further addition of chlorine water fails to impart a yellow color to the fluid. Should the experiment last several hours, the strength of the chlorine water must be determined once more at the end of the process, and the calculation of the results based upon the mean of the two experiments. Alkaline fluids must be slightly acidified with hydrochloric acid. Protoxide of iron, prot- oxide of manganese, iodine, and organic matters must not be present. Mother liquors colored yellow by organic matter should be evaporated to dryness, the residue gently ignited, then treated with water, and the fluid filtered. In evaporating the solutions to dryness, carbonate of soda must be added, since chloride and bromide of magnesium evolve hydro- chloric and hydrobromic acids in the process. II. Separation of Bromine from the Metals. The metallic bromides are analysed exactly like the corresponding chlorides ( 141, II., a to d), the whole of these methods being appli- cable to bromides as well as chlorides. In the decomposition of bromides by sulphuric acid( 141, II., d), porcelain crucibles must be used instead of platinum ones, as the liberated bromine would injuriously affect the latter. Supplement. Determination of Free Bromine. 144. Free bromine in aqueous solution, or evolved in the gaseous form, is determined in the same way as free chlorine (see 142). Another method has been proposed by Williams (" Chem. Gaz.," 1854, 432). It is based upon the fact that fi'ee bromine suffers decolorization by the action of oil of turpentine, the bromine re- placing the hydrogen in the latter 34 parts of oil of turpentine (1 equivalent) decolorize 79-97 parts (1 equivalent) of bromine. A solution of perfectly pure oil of turpentine in absolute alcohol is used as test fluid, 20 grammes of the oil being dissolved to 200 c.c. of fluid. The fluid containing the free bromine should be in a stoppered bottle. The test fluid is added drop by drop, the bottle being shaken after every addition, and the operation continued until the mixture is quite colorless. Every 34 c.c. correspond to 8 grms. of bromine. For small quantities of bromine a more dilute test fluid must be used. Results satisfactory. The determination of free bromine in presence of hydrobromic acid or metallic bromides is also effected in the same manner as that of free chlorine in presence of hydrochloric acid or metallic chlorides (see 142, 2). The addition of ammonia to the bromine requires caution. If bromine in solution is to be converted by ammonia into bromide of ammonium, the solution is poured into a capacious flask, a tolerably large quantity of water added, and then the ammonia through a funnel tube. The nitrogen gas escaping is transmitted, by means of a bent tube, through dilute ammonia ; the two fluids are then mixed 145.] -HYDRIODIC ACID. 287 together, and the remainiug part of the process is conducted as directed in 142. By this means all loss of substance is effectively guarded against. 145. 3. HYDBIODIC ACID. I. Determination. a. If you have hydriodic acid in solution, precipitate with nitrate of silver, and proceed exactly as with hydrochloric acid ( 141). For the properties of iodide of silver, see 94, 3. The results are perfectly accurate. b. The following method, recommended first by Lassaigne, is resorted to almost exclusively to effect the separation of hydriodic acid from hydrochloric and hydrobroinic acids, for which purpose it is extremely well adapted. Acidify the solution slightly with hydrochloric acid, and add a solution of protochloride of palladium, as long as a preci- pitate forms; let the mixture stand from 24 to 48 hours in a warm place, filter the russet-black precipitate off on a weighed filter, wash with warm water, and dry at a temperature from about 158 to 176 F., until the weight remains constant. The drying may be greatly facilitated by replacing the water (after the operation of washing) by some alcohol, and the latter fluid again by a little ether. For the properties of the precipitate, see 94, 3. This method gives very accurate results, provided the drying be managed with proper care; but if the temperature is raised to near 212 F., the precipitate smells of iodine, and a trifling loss is incurred. Instead of simply drying the protiodide of palladium, and weighing, it in that form, you may ignite it in a crucible of porcelain or platinum,* and calculate the iodine from the residuary metallic palladium (H. Rose). c. Kerstings volumetrical method (" Annal. der Chem. und Pharm.," 87, 25). This method is based upon the precipitation of iodine from iodide solution by protochloride of palladium. The process requires, a. A solution of pure iodide of potassium containing exactly 1 part of iodine in 1000 parts of fluid. This is prepared by dissolving 1*308 grm. of ignited iodide of potassium in water, and diluting the solution to 1 litre of fluid. (3. An acid solution of protochloride of palladium containing exactly 1 part of palladium in 2370 parts of fluid. This is prepared by dissolv- ing 1 part of palladium in nitrohydrochloric acid, with application of heat, evaporating the solution to dryness at 212 F., adding 50 parts of concentrated hydrochloric acid and 2000 parts of water, and allowing to deposit. The exact strength of the clear solution is then ascertained by means of the solution of iodide of potassium, in the manner described below (Analytical Process). y. T/ie solution of the iodide to be analysed. Dissolve the iodide in water, if possible, and determine the amount of iodine in it approximately, in the manner described below (Analytical Process) ; dilute the rest of the solution until it contains 1 part of iodine in about 1000 parts, and then determine the exact amount of iodine in it by the same method. Should the iodide be insoluble in water, or not well adapted for direct * This substance is not injured by the operation. 288 HYDRIODIC ACID. [ lib. solution, on account of foreign admixtures, distil with concentrated sulphuric acid, in a retort with the neck directed upward^ and continue the application of heat until sulphuric acid fumes begin to be evolved. Take care to add at first from 20 to 100 c.c. of fluid, 20 c.c. of sulphuric acid (free from iodine). Should the distillate contain free iodine with hydriodic acid, add 1 or 2 drops of thin starch-paste,* then aqueous solu- tion of sulphurous acid, until the blue coloration is just disappearing. If the distillate contains sulphurous acid (as is the case, for instance, when urine containing iodine is distilled with sulphuric acid), add 1 or 2 drops of starch paste, and then, cautiously, solution of chloride of lime until the fluid just begins to show a blue tint, and dispel the blue coloration again by adding 1 or 2 drops of a weak aqueous solution of sulphurous acid. If the solution contains a very large amount of free acids, neutralize the latter partly with solution of soda. The Analytical Process. Pour 10 c.c. of the solution of protochloride of palladium into a white glass flask, of from 100 to 200 c.c. capacity, dilute slightly with water, insert the cork loosely, and place the flask in a water-bath of from 140 to 212 F. Add now solution of iodide of potassium from the burette, shake, and heat a few seconds. When the fluid has cleared, which does not take long, pour some of it into 2 test tubes sufficient to fill them respectively to the height of 2 inches. By dropping some more solution of iodide of potassium into the one, and then comparing it with the other, you can readily see whether or not the iodide of potassium continues to produce a brown color in the fluid. Add now some more of the solution of iodide of potassium to the fluid in the flask, return to it also the sample from the test tubes, shake the flask, heat a few seconds, allow the fluid to become clear, test it again in the way just now described, and repeat the same process until further addition of iodide of potassium ceases to produce a coloration in the fluid. Now filter off a sample of the fluid, and test it both with protochloride of palladium and iodide of potassium ; if neither produce a perceptible brown coloration, the experiment is at an end. It will be readily understood that, should too much iodide of potassium have been added, this error must be rectified by a further addition of 1 c.c. of solution of palladium. The preliminary determination of the exact strength of the palladium solution is effected precisely in the same manner. Every 100 c.c. used of the solution of iodide of potassium (containing O'lOO of iodine) corre- spond to 0-042 grm. of palladium. According to Kersting's experiments, the following bodies exercise no adverse influence on the process: dilute hydrochloric acid, sulphuric acid, phosphoric acid, nitric acid, acetic acid, and the neutral salts of these acids with potassa, soda, and ammonia; also chloride of calcium and chloride of zinc; acetate of lead; sugar; uric acid and the distillate of urine with sulphuric acid; alcohol and ether; starch-paste; oil of lemon; also bromide of sodium, in presence of free acetic acid. The following bodies exercise an adverse influence on the process: bromide of sodium, in presence of free mineral acids, more especially upon heating; free alkalies j free chlorine, bromine, iodine, cyanogen ; a large quantity of * Kersting prepares this by boiling 1 part of starch and '1 part of sulphuric acid in 24 parts of water. 145.] HYDRIODIC ACID. 289 nitric acid, at a high temperature ; sulphurous acid. These substances dissolve iodide of palladium, and consequently prevent the precipitation. This method of Kersting's has been tested in my own laboratory, and found to give very accurate results.* d. A. and F. Dupres method (" Annal. d. Chem. u. Tharm.," 94, 365). This is based upon the same principle as Golfier-Besseyre's method (Schwarz, "Anleitung zur Maassanalyse," 1853, page 114), viz., upon the circumstance that, when chlorine water or solution of chloride of soda (Na O Cl O) is added to a metallic iodide, the first equivalent of chlorine liberates iodine,which then combines with 5 more equivalents of chlorine to pentachloride of iodine. Golfier-Besseyre uses starch-paste in the process, whilst A. and F. Dupre employ, with much better success, chloroform or bisulphide of carbon, as these two substances are colored intensely violet by free iodine as well as by all compounds of iodine with chlorine containing less than 5 equivalents of chlorine. The process may be conducted in two different ways. a. Add chlorine water to a few litres of water, and determine the chlorine in the fluid as directed in 142. Take now of the fluid under examination a quantity containing no more than about 10 milligrammes of iodine, and pour this into a stoppered bottle, add a few grammes of pure chloroform or pure bisulphide of carbon (free from sulphur and sulphxaretted hydrogen), and then gradually, drop by drop, chlorine solution, with an occasional vigorous shake of the bottle, until the violet color of the chloroform or sulphide of carbon just disappeai-s ; which point may be hit with the greatest precision. 6 equivalents of chlorine consumed in this process correspond to 1 equivalent of iodine. A still simpler way is to fix the strength of the dilute chlorine water by making it act, first upon a' known quantity of iodide of potassium, say 10 c.c. of a solution contain- ing 0-001 grm. of iodine in 1 c.c. (see 145, c, a), then upon the fluid under examination. The amount of chlorine consumed in the first ex- periment is, in that case, to the known amount of iodine as the quantity consumed in the second experiment is to x. In cases where the quantity of iodine is so considerable that sufficient of it is liberated upon the mere addition of chlorine water to impart a distinctly perceptible coloration to the fluid, it is better to delay adding the chloroform or bisulphide of carbon, until the color first produced has nearly disappeared again upon further addition of chloriue water. xThat this method cannot be employed in presence of substances liable to be acted upon by free chlorine or iodine, is self-evident ; organic matters, more particularly, must not be pi'esent. If they are, as is usually the case with mother liquors, the method /3. should be employed. ft. Add to the fluid under examination chloroform or bisulphide of carbon, then chlorine water of unknown strength, until the fluid is just decolorized. At this point all the iodine is converted into I C1 5 . Add now solution of iodide of potassium in moderate excess; this will produce for every equivalent of I C1 5 , 6 equivalents of free iodine, which remains dissolved in the fluid. Determine the liberated iodine as directed in 146, and divide the quantity found by 6 : the quotient expresses the quantity of iodine contained in the examined fluid. * For HerapatKs colorimetrical method, based upon the Palladium reaction see "Phil. Mag.," Sept., 1853, p. 183. 290 HYDRIODIC ACID. [ 145. In presence of metallic bromides, Dupre's method requires certain modifications, for which I refer to 169. This method is suited more particularly for the estimation of minute quantities of iodine. The results are most accurate.* e. Diiflos method, based upon the separation of iodine from hydriodic acid or metallic iodides by distillation with sesquichloride of iron. When hydriodic acid or a metallic iodide is heated, in a flask, with solution of pure sesquichloride of iron, the whole of the iodine escapes along with the aqueous vapour, and protocbloride of iron is formed (Fe, G1 3 + I H = Fe 2 C1 2 + Cl H + I). The iodine passing over is received either in solution of iodide of potassium, or in a measured quantity of a solution of arsenite of soda of known strength, and its quantity determined as directed 146. Schwarz (" Anleitung zur Maassanalyse, Supplement," 1853, page 20) recommends, by way of control, to determine with solution of per- manganate of potassa, the protochloride of iron in the residue in the flask; 2 equivalents of iron found in the state of protochloride correspond to 1 equivalent of iodine. The sesquichloride of iron used in the process must be free from chlorine, nitric acid, and protochloride. The best way is to prepare it with sesquioxide of iron and hydrochloric acid. The tube which conducts the iodine vapour into the receiving fluid need not dip into it. Moride's method of separating iodine will be found in 169. II. Separation of Iodine from the Metals, The metallic iodides are analysed like the corresponding chlorides. From iodides of the alkali metals containing free alkali the iodine may be precipitated as iodide of silver, by first saturating the free alkali almost completely with nitric acid, then adding solution of nitrate of silver in excess, and finally nitric acid to strongly acid reaction. If an excess of acid were added at the beginning, free iodine might separate, which is not converted completely into iodide of silver by solution of nitrate of silver. With respect to the salts insoluble in water, I have to observe that many of them are more advantageously decomposed by boiling with potassa or soda, than by solution in dilute nitric acid, the latter process being apt to be attended with separation of iodine. This applies more particularly to protiodide of palladium, and to subiodide of copper and subiodide of mercury. From iodides soluble in water, the iodine may also be precipitated as protiodide of palladium. Lastly, the base may be determined, in one portion of the compound, by heating with concentrated sulphuric acid, the iodine, in another portion, by the method I., e. * Luca ("Compt. rend.," 37, 866 ; "Journ. f. prakt. Chem.," 61, 137) recommends another method, based upon the same principle as Dupre's. Instead of chlorine water, he uses a solution of bromine of known strength ; the process is terminated when further, addition of bromine water fails to impart a color to newly added chloroform. This method is not so convenient and practical as Dwprffs. Compare also Casaseca ("Annal. deChim. et Phys.," 45, 482 ; Liebig and Kopp's " Ann. Rep.," 1855, 790.) U6.] IODINE. 291 Supplement. Determination of Free Iodine. 146. 1. Bunserfs method (" Annal. d. Chem. u. Pharm.," 86, 265). a. Principle of the Method. The theory of this simple, neat, aud accurate method, upon which a number of analytical processes are founded, is as follows : a. Iodine aud sulphurous acid decompose in presence of water to hydriodic acid and sulphuric acid (I + H O + S O 2 = H I + S 3 ) ; but, on the other hand, sulphuric acid and hydriodic acid are decomposed again into iodine, sulphurous acid, and water (H I + SO 3 = I + H O + S O 2 ). Which of these two reactions will ensue or prevail, depends upon the relative degrees of concentration of the solution. Kow, Bunsen has ascertained, by most careful experiments, that, when iodine is brought into contact with an aqueous solution of sulphurous acid containing no more than from 0'04 to 0'05 per cent, by weight of anhydrous acid, the first reaction alone takes place ; under these circumstances, therefore, 1 equivalent of iodine converts 1 equivalent of sulphurous acid into sul- phuric acid. /3. If therefore an unknown quantity of iodine, dissolved in iodide of potassium, is mixed with an excess of such highly dilute sulphurous acid of known strength, and the amount of the sulphurous acid remaining in that form then determined, the difference shows at once the amount converted into sulphuric acid, and hence also the amount of iodine. y. The strength of the dilute solution of sulphurous acid is determined by ascertaining how much of a solution of iodine of known strength is required to convert the sulphurous acid into sulphuric acid. b. Materials required. It results from a that the following fluids are required for the analytical process : a. A Solution of Iodine of known strength. This is prepared by dis- solving 5 grammes of the purest iodine dried for some time under a bell glass over sulphuric acid and chloride of calcium with the aid of a concentrated solution of pure iodide of potassium,* in a measuring flask holding 1 litre, adding water up to the litre mark, and shaking the flask until perfect intermixture has taken place. As 1000 c.c. of this solution contain accordingly 5 grammes of iodine, every c.c. contains 0-005 grm. of iodine. But as iodine mostly contains traces of chlorine, which latter agent acts upon sulphurous acid the same way as iodine, but has a different equivalent, the solution must be tested to ascertain how much absolutely pure iodine corresponds to one cubic centimetre of the iodine solution in its action upon sulphurous acid. This examination will be found in c. ft. |3. A Solution of Sulphurous Add. Saturate water completely with sulphurous acid, at the common temperature, pour the solution into bottles, close the latter tight, and place them inverted in water. Add from 35 to 40 c.c. of this saturated solution to 5000 c.c. of water. y. A Solution of Iodide of Potassium. Dissolve 1 part by weight ot pure iodide of potassium (free from iodic acid) in about 10 parts by * This solution must be colorless, and must show no brown coloration immediately after addition of hydrochloric acid. U 2 292 IODINE. [ 146, weight of water. The solution must show no brown tint, neither upon standing in the air, nor immediately after addition of hydrochloric acid. & Starch-'paste. This should be prepared fresh for every new experi- ment ; it must be very thin and almost perfectly clear. c. Preliminary Determinations. a. Determination of the relative strength of the Solution of Iodine and tlie Solution of Sulphurous Add. Measure, by means of a pipette, SO c.c. of the dilute solution of sul- phurous acid, and transfer to a flask. Add 3 or 4 c.c. of starch paste, and then the solution of iodine drop by drop, from a burette,* well stirring until the coloration produced by the last drop just remains permanent. Suppose you have used 12-5 c.c. of iodine solution to 50 c.c. of the solution of sulphurous acid, then 50 : 12-5 will indeed approximately express the relative strength of the iodine solution and the sulphurous acid, but by no means with, the degree of accuracy attainable by a second experiment, which is made as follows : Transfer about 24 c.c. of solution of iodine from a pipette to a flask, and add 100 c.c. of the solution of sulphurous acid, which will just cause the yellow color to disappear; add 3 or 4 c.c. of starch-paste, and then, with great care, some more iodine solution, until the coloration produced by the last drop just remains permanent. By now reading off the total quantity of iodine solution consumed, the relative strength of this and the sulphurous acid is learnt with the greatest accuracy. The prompt addition of the sulphurous acid solution to the iodine solu- tion, in this second experiment, effectively prevents alteration of the former by evaporation or atmospheric action. Suppose you have found the corresponding proportion between the iodine solution and sulphurous acid solution to be, 26 c.c. of the former to 100 c.c. of the latter. As the sulphurous acid solution suffers alteration from the oxidizing action of the air, this preliminary determination must be repeated before every fresh series of experiments. ft. Determination of the exact amount of iodine in the iodine solution (or, more correctly, determination of the action of the iodine solution upon sulphurous acid, &c., expressed in parts by weight of pure iodine). As the correct determination of the strength of the iodine solution is the foundation on which this analytical method rests, the greatest care must be bestowed on this part of the process. Of the various methods by which the intended end may be attained, I will describe four, all of which give very accurate results. aa. Determination of the Strength of the Iodine Solution by means of Pure Iodine. Select three well fitting watch-glasses, a, b, and c ; weigh b and c together accurately. Put about 0'5 grm. of pure dry iodine, pre- pared according to the direction of 65, 5, into a ; place the latter, with its contents, on a small piece of sheet iron, and heat gently, until thick fumes of iodine escape. Cover a now with b, and regulate the action of the heat so that the iodine will entirely, or almost entirely, * One with caoutchouc connector and clamp answers the purpose best. 146.] IODINE. 293 sublime in b. Now remove b, whilst still hot, give it a gentle swing in the air, to remove the still uncondensed iodine fumes and traces of aqueous vapor, cover with c, place under the desiccator till cold, weigh, and transfer the two watch-glasses, together with the weighed iodine, to a capacious beaker, containing a sufficient quantity of iodide of potassium solution to dissolve the whole of the iodine to a clear fluid. Add to the solution one 50 c.c. pipette after another of your sulphurous acid, until the fluid appears quite colorless after the addition of the last pipette. Suppose the weight of the iodine in 6 was 0-3 grm. (after the deduction of the tare of the two glasses 6 and c), and you have used 5 pipettes - 250 c.c. of sulphurous acid solution to effect complete decolorization. Now add to the colorless fluid 3 or 4 c.c. of starch solution, and then solution of iodine* from the burette, until the last drop just produces a permanent blue color. Suppose this takes 5 c.c. of iodine solution. The calculation is now exceedingly simple, as the following short illustra- tion will show, which is based upon the quantities supposed to have been found in the preceding experiments : 100 c.c. of sulphurous acid solution correspond to 26 c.c. of iodine solution, 250 c.c. accordingly to 65 c.c. Deducting from these G5 c.c. the number of cubic centimetres of iodine solution added in the last experiment to effect the conversion of the excess of the sulphurous acid into sulphuric acid viz., 5 c.c., we find that 60 c.c. of the iodine solu- tion have the same power of action as the weighed quantity of pure iodine used in the experiment preceding viz., 0'3 grm. Each cubic centimetre of the iodine solution corresponds, accordingly, to 0'005 grm. of pure iodine. I prefer this method to all others, as being the most practical and convenient, and giving the most accurate results. It has this great advantage over the method originally proposed by Bunsen (see 66.), that the results obtained by it are not liable to be vitiated by a possible error in the assumed equivalent number of one of the determining elements in it. 66. Determination of the Strength of tlie Iodine Solution by means of Bichromate of Potassa. This is the method originally proposed by Bunsen. It agrees in the essential points with aa, with this difference, however, that, instead of the iodine being weighed, a determinate quantity is liberated by conducting into a solution of iodide of potassium a known amount of chlorine, produced by heating a weighed quantity of bichromate of potassa with hydrochloric acid. Weigh about 0'35 grm. of pure bichromate of potassa, rendered per- fectly anhydrous by fusion at a gentle heat, and treat with pure fuming hydrochloric acid, in the manner directed in 130, d, /3. When quite cold, transfer the fluid to a beaker, and proceed exactly as in aa. 1 equivalent of K O, 2 Cr O 8 (148-67) corresponds to 3 equivalents of iodine (380-64). With proper care, this method answers very well, but it requires a more skilful manipulation than aa. It presents, also, this great disad- vantage, that, as chemists are not yet agreed on the correct equivalent * That is to say, the iodine solution, of which the exact strength is to be determined, the corresponding proportion which it bears to the sulphurous acid solution having been ascertained already in a. 294 IODINE. [ 146. of chromium, one of the principal elements on which rests the correct- ness of the results is uncertain, and may possibly be false. cc. Determination of the Strength of tJie Iodine Solution by means of Arsenions Add. This method is based upon the principle explained in section 127, 5. Prepare an arsenite of soda solution of accurately known strength, in the manner directed in 142, 1, b, by dissolving about 0*5 grm. to the volume of 250 c.c., transfer 50 c.c. of the solution to a beaker, add from 10 to 20 c.c. of a cold saturated solution of bicarbonate of soda, then a little starch-paste, and finally solution of iodine, until the blue color of the iodized starch just begins to appear. 1 equivalent of arse- nious acid (99-00) corresponds to 2 equivalents of iodine (253'76). This method, proposed and warmly recommended by Fr. Mohr, gives also satisfactory results. dd. Determination of the Strength of tlie Iodine Solution by means of Hyposulphite of Soda. See 146, 3. The iodine solution should be kept in small bottles, with well-fitting ground glass stoppers, in the cellar. By means of a correct determined standard solution of iodine, the strength of other iodine solutions, pre- pared at some after period, may always readily be determined, by simply establishing the respective power of action of the two upon equal quanti- ties of the same solution of sulphurous acid. d. The process. Weigh the iodine, best in a small flask, dissolve in the iodide of potas- sium solution prepared after b. y. (using about 5 c.c. of iodide of potas- sium solution to O'l grm. of iodine), add one pipette after another of the sulphurous acid solution, until the fluid appears quite colorless after the addition of the 1-ast pipette. Now add starch-paste, and, finally, graduated solution of iodine from the burette, until the final reaction is attained. Calculate the number of cubic centimetres of iodine solution cor- responding to the sulphurous acid consumed in the experiment, and deduct from this the number of c.c. used to effect the conversion of the excess of the sulphurous acid into sulphuric acid. The difference expresses the number of cubic centimetres of iodine solution, containing exactly the same quantity of iodine as the examined sample. To know the amount of iodine in the latter, therefore, you need simply multiply the number of cubic centimetres with the known amount of iodine in 1 c.c. As the measuring of the sulphurous acid with the pipette, or measiiring flask, is rather a tedious operation, the following apparatus may be ad- vantageously employed in laboratories where determinations of iodine by Bunseris method are of frequent occurrence. A is a large bottle, say of 10 litres capacity. Fill this nearly with water; add from 70 to 80 cubic centimetres of a saturated solution of sulphurous acid, shake the mixture vigorously, and place the bottle on a raised firmly-fixed stand. Join h to/ and g, by means of the vulcanized india-rubber tube e. and push the end of the caoutchouc tube, which projects below the compression clamp a, over the little tube opening into c d j the end of this tube is bent sideways, by which arrangement the 146.] IODINE. 295 liquid passing through it is made to flow quietly down the side of c d. The tube g contains small lumps of phosphorus interspersed between pieces of asbestos ; f contains hy- drate of potassa. The tube c d is perpendicularly fixed, by means of two iron rings (not marked in the engraving), or in some other way, to the wall, or to a proper stand, with 10 or 12 centimetres clear space between, and the o point on a level with the eye of the opera- tor. This tube is accurately gra- duated from above downward for delivering the volumes marked in it; there is no need of making the divisions smaller than 50 cubic centimetres each. To graduate the tube, fill it with water up to the zero mark and allow 50 c.c. to flow out through b, into a measuring tube accurately graduated for hold- ing the volumes marked on it (or 50 grm. of 39-2 R, or 49-95 grm. of 60-8 R, into a tared flask), and then mark the height of the fluid remaining in the tube by cutting a line with a diamond ; repeat the same operation until the tube is graduated in its whole length. The mode of using this appa- ratus is self-evident. When the tube c d is to be filled from A, the compression clamp a is opened ; when a measured quantity of sul- phurous acid is required, the com- pression clamp b. The fluid drawn through b is allowed to flow gently Fig- 72. down the side of the beaker. 2. With Arsenite of Soda and Iodine Solution. Fr. Mohr's method, slightly modified. The process requires a standard iodine solution, prepared as directed in 1 (Eunsens method), and a solution of arsenite of soda prepared as directed 142, 1, b. The relative proportion between the two is fixed according to the directions given in the same place. The sample under examination is mixed with a measured quantity of the solution of arsenite of soda, which must be slightly in excess ; starch-paste is then added, and also bicarbonate of soda, and the excess of arsenious acid determined by means of the iodine solution. If the amount consumed to oxidize the excess of the arsenious acid is deducted from the quantity of iodine solution corresponding to the arsenious acid, the difference expresses the number of cubic centimetres of iodine solution containing exactly the same amount of iodine as the examined sample, and accordingly gives also the weight of the iodine to be determined. 296 HYDROCYANIC ACID. [ 147. 3. With Hyposulphite 'of Soda (Schwarz'a method, " Anleitung zur . Maassanalyse, Supplement," 1853, page 22). This method is based upon the following reaction : 2 (Na O, S s O s ) + 1 = Na I + Na O, S 4 O 8 . 24-84 grammes of pure crystallized hyposulphite of soda are dissolved to the volume of 1 litre. 100 c.c. of the solution correspond to 1*2688, i.e., to OO'l equivalent of iodine. This solution (which according to Fr. Mohr* retains its strength, or standard, unaltered) is added to the solution of the sample in iodide of potassium, until the fluid appears of a bright yellow, thin and very clear starch-paste is then added, which must produce blue coloration, and finally again hyposulphite of soda, until the blue fluid is just again decolorized. According to Fr. Mohr, this method gives very accurate results. If a fluid contains free iodine in presence of iodine in a state of com- bination, the former is determined in one portion of the fluid, by either of the preceding methods (1, 2, or 3), and the total amount of iodine present in another portion of the fluid. To this end, sulphurous acid is added until the fluid appears colorless, and then solution of nitrate of silver (145, a); the precipitate is digested with nitric acid, to remove any sulphate of silver that might have been thrown down along with it, filtered, &c.; or the fluid is distilled with sesquichloride of iron, as directed in 145, e. 147. 4. HYDROCYANIC ACID. I. Determination. a. If you have free hydrocyanic acid in solution, mix the solution, in a rather dilute state, with solution of nitrate of silver in excess, add a little nitric acid, and determine the precipitated cyanide of silver as directed in 115, 3. If you wish to determine in this way the hydrocyanic acid in bitter almond water or cherry laurel water, add ammonia after the addition of the solution of nitrate of silver, and then supersaturate slightly with nitric acid. This modification of the process is indispensable to precipitate from these fluids the whole of the hydrocyanic acid as cyanide of silver. b. Liebigs Volumetrical Metlwd (" Annal. der Chem. und Pharm.," 77, 102). If hydrocyanic acid is mixed with potassa to strong alkaline reaction, and a dilute solution of nitrate of silver is then added, a per- manent precipitate of cyanide of silver or, if a few drops of solution of chloride of sodium have been added (which is always advisable), of chlo- ride of silver forms only after the whole of the cyanogen is con- verted into double cyanide of silver and potassium. The first drop of solution of nitrate of silver added in excess produces the permanent pre- cipitate. 1 equivalent of silver consumed in the process corresponds, therefore, exactly to 2 equivalents of hydrocyanic acid (2 K Cy + Ag O, NO 6 = Ag Cy, K Cy -t- K 0, N O 6 ). A decimal solution of nitrate of silver, containing 10797 grammes of silver in the litre, should be used ; 1 c.c. of this solution corresponds to 0'0054 of hydrocyanic acid. In examining medicinal hydrocyanic acid, 5 to 10 grammes ought to be used, but of bitter almond water about 50 grammes if exactly 5'4 or 54 grammes are used, the number of cubic centimetres consumed of the silver solu- tion, divided by 10, or by 100, expresses exactly the percentage amount of hydrocyanic acid contained in the examined sample. Medicinal * Fr. Mohr' 8 "Lehrbuch der Titrirmethode." Addition to page 332. 147.] HYDROCYANIC ACID. 297 hydrocyanic acid is suitably diluted first by adding from 5 to 8 vohimes of water; bitter almond water also, is slightly diluted ; if turbid, acobol is added until the turbidity disappears. Liebig has examined by this method hydrocyanic acid of various degrees of dilution, and has obtained results corresponding exactly with those obtained by a. In this method it does not matter whether the hydrocyanic acid contains an admixture of hydrochloric acid or formic acid. A considerable excess of potassa must be avoided. If it is intended to determine cyanide of potassium by this method, a solution of that salt must be prepared of known strength, and a measured quantity used containing about O'l grm. of the salt. Should it be mixed with sulphide of potassium, it is first freed from this, by adding a few drops of a solution of a salt of cadmium, and filtering off the precipi- tated sulphide of cadmium. c. Fordos and Geliss Volumetrical Method * (" Journ. de Chim. et de Phariu.," 23, 48. "Journ. f. prakt. Chem.," 59, 255). This method is founded upon the reaction of free iodine upon cyanide of potassium :t K Cy + 2 I = K I + I Cy. 2 equivalents of iodine = 253'76 correspond accordingly to 1 equivalent of cyanogen = 26, or to 1 equivalent of hydro- cyanic acid = 27, or to 1 equivalent of cyanide of potassium = 65-11. The iodine solution is prepared according to the directions of 146. If you have to examine free hydrocyanic acid, mix the fluid cautiously with solution of soda to alkaline reaction, add water containing carbonic acid (Selters or soda water), to convert a possible excess of alkali into bicarbonate, and then iodine solution, until a permanent yellow color is produced. For the analysis of cyanide of potassium, pi'epare a fluid of known strength, and use a volume containing 0'Q5 of cyanide of potas- sium ; addition of carbonic acid water is necessary in the process. The cyanide must contain no sulphide of potassium. The method gives satis- factory results. d. G. Mohrs MetJwd. For the principle of this method, see 119, 4, d. As the decomposition is not uniformly the same, I cannot recommend the method. II. Separation of Cyanogen from the Metals. a. In soluble Metallic Cyanides (cyanide of mercury excepted). Mix the solution of the cyanide with solution of 'nitrate of silver in excess, add nitric acid to acid reaction, and proceed as in I., a. Deter- mine the bases in the filtrate, after the removal of the excess of the salt of silver added ; see Section V. b. In insoluble Metallic Cyanides which dissolve readily in dilute Nitric Acid. Dissolve the cyanide by shaking with extremely dilute nitric acid, in a stoppered flask, add nitrate of silver in excess, and proceed as in II., a. c. In all Cyanides from ivhich the Cyanogen may be completely expelled by heating with Hydrochloric Acid. Heat the cyanide with water, in a small distillation flask, having a' burette (with caoutchouc connector and compression clamp) inserted through the cork. Let hydrochloric acid flow in in small portions, by * With regard to fferapath's colorization method, which is founded on the intensity of the color of a sulphurous oxide of iron solution, compare " Journ. f. prakt. Cliem.," 60, 242; "Phil. Mag.," Sept., 1853, vol. vi. p. 185. t Mentioned first by Servtttu and WoUer. 298 HYDROCYANIC ACID. [ 147. opening the clamp, until the fluid in the flask contains a strong excess of acid. Fit the tubulated receiver air-tight to the apparatus, and connect the tubulature, by means of a limbed tube, with a TJ-shaped tube. The latter and the receiver contain a little solution of soda. After the ter- mination of the process, treat the contents of the receiver and U tube as directed L, b. d. In all insoluble Metallic Cyanides. Ignite the cyanide, and determine the metal in the residue, either by direct weighing, or by solution in acid and precipitation. The amount of cyanogen is either inferred from the loss, or determined by the method of organic analysis. Many of the metallic cyanides may be decom- posed also by evaporation with hydrochloric acid, or by boiling with oxide of mercury. In the latter case, the oxides separate, mixed with the excess of the oxide of mercury, whilst basic cyanide of mercury dissolves. e. In Cyanide of Mercury. Precipitate the aqueous solution with sulphuretted hydrogen, and de- termine the mercury as directed in 118, 3, and the hydrocyanic acid formed as directed in 169. The cyanogen may be advantageously determined, also, in a separate portion by the method of the qualitative determination of nitrogen (184). III. Analysis of Double Protocyanides (Ferrocyanides, &c.). a. Volumetric Determination of Ferro- and Ferricyanogen. This method devised by one of the students in my laboratory, Mr. E. de Haen, is founded upon the simple fact that a solution of ferrocyanide of potassium acidified with hydrochloric acid (which may accordingly be assumed to contain free hydroferrocyanic acid), is by addition of per- manganate of potassa converted into the corresponding ferricyanide. If this conversion is effected in a very dilute fluid, containing about 0-2 grin, of ferrocyanide of potassium in a volume of from 200 to 300 cubic centimetres, the termination of the reaction is clearly and unmis- takably indicated by the change of the originally pure yellow color of the fluid to reddish-yellow. The process requires two test fluids of known strength, viz., 1. A solution of pure ferrocyanide of potassium. 2. A solution of permanganate of potassa. The former is prepared by dissolving 20 grammes of perfectly pure and dry crystallized ferrocyanide of potassium in the necessary quantity of water to give 1 litre of solution ; each c.c. of this solution therefore contains 20 milligrammes of ferrocyanide of potassium. The latter is diluted to the extent that somewhat less than a burette full is required for 10 c.c. of the solution of ferrocyauide of potassium. To determine the strength of the permanganate of potassa solution in its action upon ferrocyanide of potassium, measure off, by means of a small pipette, 10 c.c. of the solution of fei'rocyanide of potas- sium (containing 0'200 grm.) dilute with about 250 c.c. of water, acidify with hydrochloric acid, place the glass on a sheet of white paper, and allow the solution of permanganate of potassa to drop into the fluid, stirring it at the same time, until the change from yellow to reddish-ye\]ow indicates that the conversion is 147.] HYDROCYANIC ACID. 299 complete.* Kepetitions of the experiment always give very accu- rately corresponding results. As the solution of permanganate of potassa is liable to alteration, its strength must always be determined before every new series of experiments. To determine the amount of ferrocyanide of potassium contained in any given sample of the yellow salt of commerce, dissolve 5 grammes of the latter in the necessary quantity of water to give 250 c.c. of solu- tion ; take 10 c.c. of this solution, and examine as just now directed. Suppose, in determining the strength of the solution of permanganate of potassa in its action upon ferrocyanide of potassium, you have used 20 c.c., and you find now that 19 c.c. is sufficient, a simple calculation, 20 : 0-200 : : 19 : x will inform you how much pure ferrocyanide of potassium the analysed salt contains. And even this may be dispensed with, by diluting the solution of permanganate of potassa so that exactly 50 c.c. correspond to 0-200 of ferrocyanide of potassium, as, in that case, the number of half- cubic centimetres consumed expresses directly the percentage amount of the ferrocyanide of potassium present in the analysed salt. Instead of determining the strength of the permanganate of potassa solution by means of pure ferrocyanide of potassium, which is unques- tionably the best way, one of the methods given in 112, 2 may also be employed ; bearing in mind, in that case, that 2 equivalents of ferro- cyanide of potassium = 422-44 (together with the water of crystallisation), 2 equivalents of iron dissolved to protoxide = 56, and 1 equivalent of oxalic acid = 63 (together with the water of hydration and crystallisation) are equivalent in their action upon solution of permanganate of potassa. The analysis of soluble ferricyanides by this method is effected by reducing them to ferrocyanides, acidifying, and then proceeding in the same way as just now described. The reduction is effected as follows : Mix the weighed ferricyanide with solution of soda or potassa in excess, boil, and add concentrated solution of sulphate of protoxide of iron gradually, and in small portions, until the color of the precipitate appears black, which is a sign that protosesquioxide of iron has pre- cipitated. Dilute now to the volume of 300 cubic centimetres, and proceed to determine the ferrocyanide in portions of 50 or 100 c.c. of the fluid. As the space occupied by the precipitate is not taken into ac- count in this process, the results are not absolutely accurate. The dif- ference is so very trifling, however, that it may safely be disregarded. Insoluble ferro- or ferricyanides, decomposable by boiling solution of potassa (as are most of these compounds), are analysed by boiling a weighed sample sufficiently long with an excess of solution of potassa (adding, in presence of ferricyanides, sulphate of protoxide of iron), and then proceeding in the same way as directed above. Ferricyanides may be analysed also by another method, also de- vised by one of the students in my laboratory, Mr. E. Lenssen. It is founded on the fact that, when ferricyanide of potassium, solution of iodide of potassium, and concentrated hydrochloric acid are mixed together, 1 equivalent of iodine = 126-88 separates for every equivalent of ferricyanide of potassium = 329-5 (Cfdy, H 8 ) + 1 H = 2 (Ofy H 2 ) + I. * If you wish for some additional evidence besides the change of color, add to a drop of the mixture on a plate, a drop of solution of sesquichloilde of iron : if this fails to pro~ duce a blue tint, the conversion is accomplished. 300 HYDROSULPHURIC ACID. [ 148. - By determining the liberated iodine by Bunsens method ( 146), we learn the quantity of the ferricyanide of potassium. Lenssen obtained in 4 experiments respectively, 99-22, 101-7, 102-1, 100-5, instead of 100. b. Methods based upon tlie Destruction of the Cyanogen. a. Eolleys method (" Annal. d. Chem. u. Pharm.," 87, 254). Mix a weighed sample of the dried double cyanide with 3 or 4 times the quantity of a mixture of 3 parts of sulphate and 1 part of nitrate of ammonia ; transfer the powder to a small tubulated retort, rinse the mortar, &c., with the mixture of the two ammonia salts, add the rinsings to the powder in the retort, join a receiver loosely to the neck of the latter, and heat over a spirit-lamp, shaking the mixture occasionally. Complete decomposition ensues even at a moderate heat, attended with glimmering of the mass ; the whole of the cyanogen volatilizes in the form of cyanide of ammonium and of the products of the decomposition of the latter substance, whilst the metals remain as sulphates. As traces of these may have been carried over into the receiver, evaporate the fluid contained in the latter in a poi-celain dish, volatilize the ammonia salts (if necessary), and dissolve what remains in the receiver in a little nitric acid. Dissolve the residue in the retort in water, adding, if necessary, some nitric acid, and then separate the metals in the clear solution by the appropriate methods, which are given in Section V. Bolley says he obtained very accurate results by this simple and easy method, in the decomposition of various ferro- and ferricyanides. ft. Glaus ( Jahresbericht v. Liebig and Xopp, 1855, 816) recommends to decompose the double protocyanide of platinum and the alkali metals by heating a mixture of 1 part of the salt with 4 parts of nitrate of suboxide of mercury, in small portions, in a platinum crucible. The mass defla- grates feebly; the platinum and alkali are easily determined in the residue, after volatilization of the oxide of mercury. y. The estimation of the nitrogen and carbon (cyanogen) in such com- pounds is effected by the methods given in Section VI. (Ultimate or Elementary Analysis of Organic Bodies). c. Determination of the Alkalies, more particularly of Ammonia in soluble Ferrocyanides. Mix the boiling solution with solution of chloride of copper in moderate excess, filter the precipitated ferrocyanide of copper, free the filtrate from copper by sulphuretted hydrogen, and then determine the alkalies (Reindel, " Journ. f. prakt. Chem.," 65, 452). 148. 5. HYDROSULPHURIC ACID (Sulphuretted Hydrogen). I. Determination. Sulphuretted hydrogen in the free state is most readily and very accurately determined by volumetric analysis, by means of iodine ; the sulphur in it may also be determined by converting it into a suitable sulphide or into sulphate of baryta, and weighing. a. The method of determining free sulphuretted hydrogen by volu- metric analysis, by means of a solution of iodine, was employed first by Dupasquier. That chemist used alcoholic solution of iodine for the ' 14:8.] HYDROSULPHURIC ACID. 301 purpose. But as the action of the iodine upon the alcohol gradually alters the composition of this solution, it is better to use a solution of iodine in iodide of potassium. The decomposition ensues according to the formula : 1 equivalent of 1 = 126-88 corresponds to 1 equivalent of HS^IT. However, this exact decomposition can be relied upon with certainty only if the amount of sulphuretted hydrogen in the fluid to be analysed does not exceed 0-04 per cent. (Bunsen). Fluids containing a larger proportion of sulphuretted hydrogen must therefore first be diluted to the required degree with boiled water free from air, and cooled out of the contact of air. The iodine solution of 146 may be used for the estimation of larger quantities of sulphuretted hydrogen; for weak solutions, e.g. sulphu- retted mineral water, it is advisable to dilute the iodine solution of 146 to 5 times the volume, which accordingly will give a fluid con- taining about O'OOl gnu. of iodine in the cubic centimetre. The process is conducted as follows: Measure or weigh a certain quantity of the sulphuretted water, dilute, if required, to the proper degree with boiled water free from air, and cooled out of the contact of air, add some thin starch-paste, and then solution of iodine, with constant shaking or stirring, until the permanent blue color of iodized starch begins to appear. The result of this experiment in- dicates approximately, but not with positive accuracy, the relative or corresponding proportion between the examined water and the iodine solution. Suppose you have consumed, to 220 cubic centimetres of sulphuretted water, 12 cubic centimetres of a solution of iodine con- taining 0'000918 grm. of iodine in the cubic centimetre.* Introduce now into a flask nearly the quantity of iodine solution required, weigh, add sulphuretted water until the fluid is just decolorized, insert the stopper, and weigh again ; then add starch-paste, and after this iodine solution until the blue color of iodized starch just begins to show. By this course of proceeding, you avoid the loss of sulphuretted hydrogen which would otherwise be caused by evaporation and oxidation. Instead of determining the quantity of the sulphuretted water by weight, it may be determined also, in a suitable way, by measure. In my analysis of the Weilhach water. 256 c.c. of the water required, in my second experiment, 16'20 c.c. of iodine solution, which, calculated upon the quantity of sulphuretted water used in the first experiment, viz , 220 c.c., makes 13-9 c.c., or 1-9 c.c., more than was used in the first experiment in which chance of loss by evaporation or oxidation had not been guarded against by the course of proceeding adopted in the second. But even now the experiment cannot yet be considered quite conclu- sive, when made with a very dilute solution of iodine, as in the case given here by way of illustration ; but it is still necessary to ascertain how much iodine solution is required to impart the same blue tint to the same quantity of a similar mixture of starch and ordinary water oiHhe same temperature, and as nearly as possible the same state and condition as the analysed sulphuretted water (comp. " Annal. d. Chem. u. Pharrn.," 102, 186), and to deduct this from the quantity of * The numbers here stated are those which I obtained in the analysis of the Weilbach water. 302 HYDROSULPHUKIC ACID. [ 148. iodine solution used in the second experiment. Thus in my analysis of the Weilbach water, I had to deduct 0-5 c.c. from the 16-20 c.c. consumed in the second experiment. If the instructions here given are strictly followed, this method gives very accurate results (see Analytical Notes and Experiments, No. 86). b. Fr. Mohr's method slightly modified. Mix the sulphuretted fluid with a slight excess of solution of arsenite of soda of known strength (determined by means of iodine solution, see 142, 6), and add hydrochloric acid to distinct acid reaction. Dilute to the volume of 300 cubic centimetres, pass through a dry filter, test a sample of the filtrate with sulphuretted hydrogen, to make quite sure that it still contains arsenious acid, and then determine in 100 c.c., after addition of powdered bicarbonate of soda, the remainder of the arsenious acid left in it. Deduct the quantity of iodine solution consumed in the last part of the process, multiplied by 3 (as only 100 of the 300 c.c. have been operated upon), from that which would have been required to effect the decomposition of the entire quantity of arsenious acid used in the process : the difference expresses the quantity of iodine solution corresponding to the sulphuretted hydrogen contained in the analysed fluid. In making the calculation, bear in mind that 2 equivalents of iodine will now correspond to 3 equivalents of H S, since 1 equivalent of As O 3 decomposes, on the one hand, 3 H S to As S 3 and 3 H O, and requires, on the other hand, 2 equivalents of iodine for its conversion into arsenic acid. Very dilute solutions of sulphuretted hydrogen cannot be analysed by this method, as the sulphide of arsenic separating from them takes a very long time to deposit, and a minute portion of it invariably remains in solution.* c. Mix the hydrosulphuretted fluid with an excess of solution of arsenite of soda, add hydrochloric acid, let deposit, and determine the sulphide of arsenic as directed 127. If the quantity of sulphuretted hydrogen in the analysed fluid is moderately large, the results obtained by this method are accurate (comp. Analytical Notes and Experi- ments, No. 86) ; but in the case of very dilute solutions, the results are too low, as a little tersulphide of arsenic i-emains in solution. In my analysis of the Weilbach water, this method gave, therefore, only 0-006621 and 0-006604 per mil., whilst a (Determination by Solution of Iodine) gave 0-007025 of H S per mil. Instead of arsenious acid, solution of chloride of copper or of nitrate of silver may be employed as precipi- tant, and the sulphur determined in the sulphide of copper as sulphate of baryta ( 148, II.), or in the sulphide of silver as chloride of silver. The results obtained by precipitating with chloride of copper are also too low, in the case of very dilute fluids. As regards precipitation by silver solution, I cannot yet speak from actual experience. Lyte (" Compt. rend.," 43, 765) recommends solution of chloride of silver in hypo- sulphite of soda, mixed with a few drops of ammonia, as the most suitable for the purpose. For the analysis of mineral waters, the method a will always answer best, unless presence of hyposulphites should impair its accuracy. d. If the sulphuretted hydrogen is evolved in the gaseous state, the best way is to conduct it first through several U-tubes, containing au * A solution containing in the litre 0'003 H S gave with, a solution of arsenious acid in hydrochloric acid, only after twelve hours, a precipitate admitting of filtration. 148.] HYDROSULPHTJRIC ACID. 303 alkaline solution of arseuite of soda, then through a tube connected with the exit-mouth of the last U-tube, which contains pieces of glass moistened with solution of soda; to mix the fluids afterwards, and proceed as in b or c. II. Separation and Determination of the Sulphur in Metallic Sulphides. 1. Methods in t/ie Dry Way. a. In all Sulphides which lose no Sulphur by the Action of Heat. Mix a weighed quantity of the pulverized substance with 3 parts of anhydrous carbonate of soda and 4 of nitrate of potassa, with the aid of a rounded glass rod, wipe the particles of the mixture which adhere to the rod, carefully off against some carbonate of soda, and add this to the mixture. Heat the latter in a platinum or porcelain crucible (which, how- ever, is somewhat affected by the process), at a gradually increased tem- perature to fusion ; keep the mass in that state for some time, then allow it to cool, heat the residue with water, filter, and determine in the filtrate, which contains the whole of the sulphur as alkaline sulphate, the sulphuric acid as directed in 1 3 The metal, metallic oxide, or carbonate, which remains undissolved, is determined, according to cir- cumstances, either by direct weighing or in some other suitable way. b. In Metallic Sulphides which lose Sulphur by tlie Action of Heat. Mix the finely pulverized compound with 4 parts of carbonate of soda, 8 of nitrate of potassa, and 24 of pure and perfectly dry chloride of sodium, and treat the mixture as in a. Or, mix the very finely pulverized substance with 3 parts of pure carbonate of soda and 3 of pure chlorate of potassa, put the mixture into a tube of difficultly fusible glass, sealed at one end, fill the fore part of this tube with car- bonate of soda mixed with a little chlorate of potassa, and heat in a combustion furnace in the same way as in organic analysis. Treat the ignited saline mass as in a. The solution will, of course, contain silicic acid from the glass (Kemp}. c. In Sulphur Salts of more Complex Composition (Berzelius and H. Rose). Use the apparatus illustrated by Fig. 73, or one of similar con- struction. Fig. 73. a is a flask from which a slow current of chlorine is evolved ;* b serves to convey into a additional portions of hydrochloric acid ; c contains con- * Pour & perfectly cold mixture of 45 parts of sulphuric acid and 21 of water, over one of 18 parts of powdered chloride of sodium and 15 of finely powdered binoxide of man- ganese, and shake, when a steady evolution of chlorine will at once begin, which, when it shows signs of slackening, may be promoted by a gentle heat. 304 HYDROSULPHTJRIC ACID. [ US. centrated stilphuric acid, d chloride of calcium both intended for drying the chlorine evolved ; e is a bulb-tube intended to receive the substance to be analysed; this tube reaches to near the surface of the water in/ (in presence of antimony, a solution of tartaric acid in dilute hydro- chloric acid is substituted for the water in /) ; the flask/ is connected with h, the connecting tube reaching down to the bottom of the fluid in the latter ; the chlorine issuing from h is conducted into niilk of lime, or into alcohol, or into the open air. When the apparatus is arranged, the sulphide to be examined is weighed in a narrow glass tube, sealed at one end, and subsequently cautiously transferred from this tube to the bulb e, in the manner illustrated by Fig. 74, to -prevent any portion of the substance getting into the ends of the bulb-tube. When the apparatus is filled with chlorine, e is connected with d by means of a vulcanized india-rubber tube, and the chlorine is allowed to act on the sulphide, at first without the aid Fig. 74. of heat. When no further alteration is ob- served, a very gentle heat is applied to the bulb, care being taken also to keep the tube g warm, securing it thus from being stopped up by the sublimate of a volatile metallic chloride. The sulphide is completely decomposed by the chlorine, the metals being converted into chlorides, which partly remain in the bulb, partly (viz. the volatile ones, as chloride of antimony, chloride of arsenic, chloride of mercury) pass over into the receiver ; the sulphur combines with the chlorine to chloride of sulphur, which passes over into the flask/ where, coming in contact with water, it decomposes with the latter, forming hydrochloric acid and hyposulphurous acid, with separation of sulphur. The hyposulphurous acid decomposes again into sulphur and sulphurous acid, which latter is finally, by the action of the chlorine water in/ con- verted into sulphuric acid. The final result of the decomposition is con- sequently sulphuric acid and a greater or less amount of separated sulphur. The operation is concluded when no more products of distillation with the exception, perhaps, of sesquichloride of iron, the complete expulsion of which need not be awaited pass over from the bulb. Heat is then applied to e, pi-oceeding from the bulb towards the bend, so as to force all the chloride of sulphur which may remain in that part to pass over into/ The apparatus is left undisturbed a short time longer, after which the tube e is cut off under the bend at g, and the separated end, which con- tains a portion of the volatile chlorides, closed by inverting over it a glass-tube sealed at one end and moistened inside. The whole is now allowed to stand 24 hours, to allow the volatile chlorides to absorb moisture, which will render them soluble in water without gene- rating heat. The metallic chlorides in the cut-off end of the tube are then dissolved in dilute hydrochloric acid, the end is rinsed, and the solution added to the contents of the flasks / and h ; a very gentle heat is now applied until the free chlorine is expelled, and the fluid is then allowed to stand until the sulphur has solidified. The sulphur is filtered off on a weighed filter, washed, dried, and weighed. The filtrate is precipitated with chloride of barium ( 132), by which operation the amount of that portion of the sulphur is determined which has been . 148.] HYDROSULPHUEIC ACID. 305 converted into sulphuric acid. The fluid filtered off from the sulphate of baryta contains, besides the excess of chloride of barium added, also the volatile metallic chlorides ; which latter are finally determined in it by the proper methods, which will be found in Section V. The chloride remaining in the bulb-tube is either at once weighed as such (chloride of silver, chloride of lead), or where this is impracticable as in the case of copper, for instance, which remains partly as subchlo- ride partly as chloride it is dissolved in water, hydrochloric acid, nitro- hydyochloric acid, or some other suitable solvent, and the metal or metals in the solution are determined by the methods already described, or which will be found in Section V. To be enabled to ascertain the weight of the bulb-tube containing the chloride of silver or chloride of lead, it is advisable to reduce the chlorides by hydrogen gas, and then dissolve the metals in nitric acid. 2. Methods in the Humid Way. a. Oxidation of the Sulphur by Acids yielding Oxygen* a. Weigh the finely pulverized sulphide in a small glass tube sealed at one end, and drop the tube into a tolerably capacious strong flask with glass stopper, which contains red fuming nitric acid (perfectly free from sulphuric acid) in more than sufficient quantity to effect the decomposition of the sulphide. Immediately after having dropt in the tube, close the flask. When the action, which is very impetuous at first, has somewhat abated, shake the flask a little ; as soon as this operation ceases to cause renewed reaction, and the fumes in the flask have condensed, take out the stopper, rinse this with a little nitric acid, letting the rinsings run into the flask, and then heat the latter gently. aa. The whole of the Sulphur has been oxidized, the Fluid is perfectly clear, t Dilute with much water, and determine the sulphuric acid formed as directed in 132. Do not neglect to wash the precipitate thoroughly with hot water, and to ascertain, after weighing, whether it is abso- lutely insoluble in dilute hydrochloric acid. Separate the bases in the filtrate from the excess of the salt of baryta by the proper methods, which will be found in Section V. bb. Undissolved Sulphur floats in the Fluid. Add chlorate of potassa in small portions, or strong hydrochloric acid, and digest some time on a water-bath. This process will often succeed in dissolving the whole of the sulphur. Should this not be the case, and the undissolved sulphur appear of a pure yellow color, dilute with water, collect on a weighed filter, wash carefully, dry, and weigh. After weighing, ignite the whole, or a portion of it, to ascertain whether it is perfectly pure. If a fixed residue remains (consisting commonly of quartz, gangue, &c., but possibly also of sulphate of oxide of lead, sul- phate of baryta, &c.,) deduct its weight from that of the impure sul- phur. In the filtered fluid, determine the sulphuric acid as in aa, calculate the sulphur in it, and add the amount to that of the un- * In presence of lead, baryta, strontia, lime, tin, and antimony, method b is preferable to a. * t This can of course be the case only in absence of metals forming insoluble salts with ; sulphuric acid. If such metals are present, proceed as in bb, as it is in that case much more difficult to judge whether complete oxidation of the sulphur has been attained. II. X 806 HYDROSULPHUEIC ACID. [ 148. ijjj dissolved sulphur. If the residue left upon the ignition of the un- dissolved sulphur contains an insoluble sulphate, decompose this as directed in 132, and add the sulphur found in it to the principal amount. In the presence of bismuth, the addition of chlorate of potassa or of hydrochloric acid is not advisable, as chlorine interferes with the deter- mination of bismuth. ft. Mix the finely pulverized metallic sulphide, in a dry flask, by shaking, with chlorate of potassa (free from sulphuric acid), and add concentrated hydrochloric acid in small portions. Cover the flask with a watch-glass, or with an inverted small flask. When the whole of the chlorate of potassa is decomposed, heat gently on the water-bath, until the fluid smells no longer of chlorine. Proceed now as directed in a, aa, or bb, according to whether the sulphur is completely dissolved or not. In the latter case you must of course immediately dilute and filter. The oxidation of the sulphur may be effected also by heating with nitric acid and chlorate of potassa. y. Strong nitrohydrochloric acid is also often used instead of the oxidizing agents named in a and /3 ; however, with this the complete conversion of the sulphur into sulphuric acid succeeds more rarely. b. Oxidation of the Sulphur by Chlorine in Alkaline Solution (Rivot, Beudant, and Daguin's Method, suitable, also, for determining the sulphur in native brimstone. (" Compt. Rend.," 1853,835. " Journ. f. prakt. Chern.," 61, 134). Heat the very finely pulverized sulphide or crude sulphur, for several hours with solution of potassa, free from sulphuric acid (which dissolves free sulphur, as well as the sulphides of arsenic and antimony), and then conduct chlorine into the fluid. This speedily oxidizes the sulphur ; the sulphuric acid formed combines with the potassa to sulphate, which dis- solves in the fluid, whilst the metals converted into oxides remain undis- solved. Filter, acidify the alkaline filtrate, and precipitate the sulphuric acid from it by chloride of barium ( 132). Arsenic and antimony pass into the alkaline solution in the form of sulphur acids, but not so lead, which is converted into binoxide, and remains completely undissolved. This method is, therefore, more particularly suited in presence of sulphide of lead. In presence of sulphide of iron, sulphate of potassa is formed at first, and hydrate of sesquioxide of iron, which, if the action of the chlorine is allowed to continue, will be converted into ferrate of potassa. As soon, therefore, as the fluid commences to acquire a red tint, the transmission of chlorine must be discontinued, and the fluid gently heated for a few moments with powdered quartz, to decompose the ferric acid formed. It occasionally happens, more particularly in presence of quartz sand, iron pyrites, oxide of copper, &c., that the process is attended with im- petuous disengagement of oxygen, which almost completely prevents the oxidizing action of the chlorine. However, this accident may be guarded against by reducing the substances to be analysed to the very finest powder. c. Determination of the sulphur in dissolved sulphides of the alkalies and alkaline earths.* * Sulphides containing hyposulphite or sulphate are analysed as directed 168. 149.] NITRIC ACID. 307 a. If the salts contain no excess of sulphur, the best way is to proceed as directed 148, 1, b, or c. . If they contain an excess of sulphur, method II., b, is the most suitable. y. In either case, the bases are estimated best in a separate portion, which is decomposed by evaporation with hydrochloric acid or sulphuric acid. THIRD GROUP. NITRIC ACID. CHLORIC ACID. 149. 1. NITRIC ACID. I. Determination. Free nitric acid in a solution containing no other acid is determined most simply in the volumetric way, by neutralizing with a dilute solu- tion of soda of known strength (compare Special Part, Section " Acidimetry"}. The following method also effects the same purpose : mix the solution, with baryta water, until the reaction is just alkaline, evaporate slowly in the air, nearly to dryness, dilute the residue with water, filter, wash the carbonate of baryta formed by the action of the carbonic acid of the atmosphere upon the excess of the baryta water, add the washings to the filtrate, and determine in the latter the baryta as directed in 101. Calculate for each equivalent of baryta found an equivalent of nitric acid. The correctness of the results depends entirely upon the accuracy of the execution of the analytical process. Avoid the use of a large excess of baryta water, and take care not to filter the evaporated fluid before its alkaline reaction has completely disappeared. II. Separation of nitric acid from the bases, and determination of tlte acid in nitrates. The determination of nitric acid in nitrates remains still a difficult problem, which has of late years much occupied the attention of chemists. Before entering upon the consideration of the question, I would lay it down as a general rule, that whatever method may be selected, it should always first be tried repeatedly upon weighed quantities of a pure nitrate, to acquire some familiarity with the details of the rather complicated processes required for the analysis of nitrates. a. Methods based upon t/te decomposition of the Nitric acid by proto- chloride of iron. a. Pelouze (" Journ. f. prakt. Chem.," 40, 324), was the first to turn the action of free nitric acid upon protochloride of iron to account for the deter- mination of nitric acid. The formula of the decomposition is as follows: 3 FeCl + N O In Pelouze's method a weighed quantity of protochloride of iron in excess is used, and the portion which remains unchanged determined by solution of permanganate of potassa. The process is conducted as follows: Dissolve 2 grammes of pianoforte wire in 80 100 c.c. of pure concentrated hydrochloric acid, in a flask holding about 150 c.c., which is closed by a cork with a glass tube fitted in it ; promote the solution by application of a gentle heat. When the wire is dissolved, add 1-2 grm. of the nitrate of potassa or an equivalent quantity of another nitrate to be analysed, replace the cork, and heat rapidly to 808 NITKIC ACID. [ 149. boiling. After 5 or 6 minutes, pour the fluid, which has now again cleared, into a larger-sized flask, dilute largely with water, and proceed as directed 112, 2, a. Though this method gives occasionally satis- factory results, it can never be fully relied on, in which view all agree who have subjected the question to a critical examination (compare Fr. Mohr, "Lehrbuch der Titrirmethode," I., 216 ; Abel and Bloxatn, " Quart. Journ. of Chem. Soc.," IX., p. 97). The results of numerous experiments made in my own laboratory lead to the same conclusion. The following may be mentioned as causes of the defectiveness of the method : a. Action of the air upon the nitric oxide gas present in the flask, together with aqueous vapor, which leads to the re-formation of nitric acid ; this may be held to be the principal cause of the inaccuracy of the .method. b. Incomplete expulsion of the nitric oxide from the fluid, which leads to the reduction of a larger amount of permanganate of potassa solution, than corresponds to the protochloride of iron ; this is to be apprehended only in the case of dilute solutions. c. Escape of nitric acid before it has acted upon the protochloride of iron ; this is to be apprehended in cases where the fluid, after addition of the nitrate, is boiled very rapidly, and the excess of protochloride of iron is comparatively small. d. Occasionally also loss of iron, owing to want of proper care in boiling, and to be apprehended more especially if part of the protochloride of iron deposits on the sides of the vessels above the fluid, in the solid state. I have succeeded in modifying Pelouze's process so as to avoid all these sources of error, and to obtain perfectly accurate and reliable results. My process is conducted as follows : Select a long-necked tubulated retort of about 200 c.c. capacity, and fix it in a slightly slanting position. Introduce into the body of the retort about 1*5 grm. of fine pianoforte wire, accurately weighed, and add about 30 or 40 c.c. of pure fuming hydrochloric acid. Con- duct now through the tubulature, by means of a glass tube reaching only about 2 centimetres into the retort, hydrogen gas washed by trans- mission through solution of potassa, and connect the neck of the retort with a TJ-tube containing some water. Place the body of the retort on a water- bath, and heat gently until the iron is dissolved. Let the con- tents of the retort cool in the current of hydrogen gas j increase the latter, and drop in, through the neck of the retort, into the body, a small tube containing a weighed portion of the nitrate under examina- tion, which should not contain more than about 0'200 grm. of nitric acid. After restoring the connection between the neck and the U-tube, heat the contents of the retort in the water-bath for about a quarter of an hour, then remove the water-bath, heat with the lamp to .boiling, until the fluid, to which the nitric oxide gas absorbed had imparted a dark tint, shows the color of sesquichloride of iron, and continue boiling for some minutes longer. Care must be taken to give the fluid an occasional shake, to pi-event the deposition of dry salt on the inner side of the retort. Before you discontinue boiling, increase the current of hydrogen gas, that no air may enter through the U-tube when the lamp is removed. Let the contents cool in the current of hydrogen gas, dilute copiously with water free from air, and determine the iron still present as protochloride by permanganate of potassa solution 149.] NITRIC ACID, 309 168 of iron converted by the nitric acid from the state of proto- to that of sesquichloride correspond to 54 of nitric acid. Direct experi- ments, made with pure nitrate of potassa, gave 10O1 - 100*03 - 100*3, and 100*5, instead of 100 of nitric acid (see Experiments, No. 87). 0. Schlosing's method ("Annal. de Chim.," 3 se~r. torn. ' 40, 479; " Journ. f. prakt. Chem.," 62, 142. The following method, employed by Schl6si,ng, more particularly to determine nitric acid in tobacco, and which affords this very important advantage, that it may be used also in presence of organic matters, has successfully passed through the ordeal of numerous and searching experiments. Fig. 75. The process is conducted in the apparatus shown in Fig. 75. The dissolved nitrate is introduced into the balloon A, whose neck is connected, by means of a vulcanized india-rubber tube a, with a narrow glass-tube b ; c is another narrow caoutchouc-tube connected with b, and 15 centimetres long. The solution of the salt, which must be neutral or alkaline, is boiled down to a small volume, the aqueous vapor completely expelling the air from A and the tubes ; c is dipped into a glass containing a solution of protochloride of iron in hydrochloric acid ; the lamp removed, and the receding of the acid regulated by compressing the caoutchouc tube c with the fingers ; when the iron solution is nearly absorbed, some hydrochloric acid is allowed to recede, three or four times, in separate portions, to free the tube completely from probo- chloride of iron, which is absolutely necessary. Before air can force its way, c is closed by an iron compression clamp, dipped under the mercury in the trough, with the end placed under the bell B. The lamp is now replaced under A, to allow the reaction to proceed ; imme- diately after, the clamp is opened, and the tube simply compressed by the fingers, which are also removed from it as soon as a pressure is felt from within. The reaction is generally terminated in about eight minutes, when c is removed from under B. The latter is a small bell- jar, made in the form of an adapter ; it must hold three or four times the volume of the gas to be received in cases where the evolution of gas is rather impetuous, it is occasionally necessary to submerge the bell- jar in the trough, to effect a more speedy cooling of the vapor. The 310 NITRIC ACID. [ 149. tipper part of B is drawn out, as shown in Fig. 76, to facilitate the in- sertion of the neck c of the caoutchouc-tube, and also the breaking off the point. The bell-jar is first filled with water, to expel the air from it, then with mercury ; milk of lime, previously boiled, is then finally introduced into it, by means of a curved pipette, which serves to free the nitric oxide gas entering B from every trace of acid vapor. The nitric oxide gas has now to be transferred to another balloon, c, to be there reconverted into nitric acid by oxygen. The balloon c contains some water ; it is connected by a caoutchouc-tube, d, with a glass-tube, e, which bears at the opposite end another thin caout- chouc-tube,^ 10 centimetres in length. The water in c is now heated to boiling, until all air is expelled from the balloon and the tubes by the aqueous vapor ; / is connected with the point of the bell-jar, B, which has just before been slightly cut with a diamond, and the end of the point then broken Fig. 76. off. The aqueous vapor condenses at first in the bell- jar, which serves also to expel the small quantity of milk of lime remaining in the point. But if the lamp is now removed, a current in the opposite direction speedily sets in, which drives the nitric oxide gas into the balloon, c. Should this proceed too rapidly, / need simply be compressed with the fingers. As soon as the milk of lime in the bell-jar has nearly reached the rim of c,/is closed by a compression clamp. To transfer the last traces of the nitric oxide gas to c, pure hydrogen gas (20 or 30 c.c.) is conducted into the bell-jar, and allowed to be absorbed as before. / is then closed by the compression clamp, the end of the tube taken off from the point of the bell-jar, and connected instead with the glass-tube, h, of the oxygen-jar, D ; the cork, r, is now opened, and then the compression clamp also, which will cause oxygen to pass from the jar into the balloon, c. When the object of the operation has been attained, r is closed, and h and / are discon- nected ; after waiting a quarter of an hour, the free nitric acid repro- duced in o is determined by means of very dilute solution of soda ( 215). The success of this method depends essentially upon the complete expulsion of the air from A and c. Schlosing obtained highly satisfactory results by it. Where the quantity of nitric acid is only small, it is advisable to increase the amount of protochloride of iron considerably. For the determination of very minute quantities of nitric acid (under 0-010 grm., Schlosing employs a somewhat modified apparatus, for a description of which I refer to his paper on the subject, in the " Annal. de Chim.," 3 ser. torn. 40, 479. y. Fife's method (" Compt. rend.," 41, 939 and 987). In this method, the nitric oxide gas evolved from the nitrate by pro- tochloride of iron and hydrochloric acid is converted into ammonia, which is then received in a standard acid, as in 99, 3. Small quantities of nitric oxide (obtained from 0'5 grm. or less of nitrate of potassa), are converted into ammonia by conducting the disengaged gas, mixed with an excess of hydrogen gas, over spongy platinum, heated nearly to red- ness ; larger quantities, by conducting the gas, mixed with an excess of sulphuretted hydrogen, over soda-lime heated nearly to redness (N O a + 149.] NITRIC ACID. 311 3 H S + 2 Ca O = N H 3 + Ca O, S O 3 + Ca S 2 ). Fig. 77 shows the plan of the apparatus required. F is an apparatus for the evolution of hydro- gen, E, the washing-bottle belonging to it ; D serves for the reaction of the nitrate on the protochloride of iron ; c is a sulphuretted hydrogen apparatus ; B, the washing-bottle belonging to it. The glass tubes pro- ceeding from B and D lead to the flask A, where they dip under mercury ; a few pieces of chloride of calcium are placed in the mercury to retain the water which finds its way into A. The tube proceeding from A leads to another, which contains soda-lime, and is placed in a combustion- furnace ; the free end of the latter tube is afterwards connected with a Varrentrapp and WilFs absorption apparatus, which contains a measured quantity of acid of known strength ( 187). When the apparatus is prepared, solution of protochloride of iron in an excess of hydrochloric acid is introduced into D, to the amount of, at least, 100 grammes ; if much organic matter is present, as in the case of molasses, ( for instance, it even requires as much as 300 or 400 grammes of a saturated solution of protochloride of iron, together with 3 or 4 grammes of concentrated hydrochloric acid. If there is much frothing of the organic matter, some butter should be added. The nitrate is now introduced into the flask D, and hydrogen transmitted through it for 10 minutes, to expel the air ; after some time, the tube with the soda- lime is also heated, and, as soon as no more aqueous vapors are observed, connected with the absorption-apparatus, the transmission of hydrogen being continued, but at a slower rate. Sulphuretted hydrogen is now also evolved in c, and heat shortly after applied to D, so that by the time the contents begin to boil, about 3 or 4 centimetres of the soda-lime are decomposed. The evolution of sulphuretted hydrogen must now proceed briskly, the bubbles of gas following each other in rapid succes- sion. After 10 minutes' boiling, the disengagement of sulphuretted hydrogen is discontinued, hydrogen being then still transmitted through the apparatus for 4 or 5 minutes. At least 15 centimetres of the soda- lime must remain undecomposed. When the operation is terminated, the contents of the nitrogen bulbs are determined as directed in 99, 3. Vitte has tried this method on nitrate of potassa with very satisfactory results. b. Metlwd based upon the oxidation of Arsenious to Arsenic Acid. . Mix the compound with 3 times its weight of arsenious acid ; dissolve the mixture in concentrated hydrochloric acid, evaporate to dryness, dissolve the residue in water, supersaturate the solution with ammonia, precipitate with a mixture of chloride of ammonium and sulphate of magnesia, and determine the precipitated arsenate of ammonia and magnesia as directed in 127, 2, a (J. Stein). The results are accurate ; comp. Analytical Notes and Experiments, No. 88. c. Method based upon measuring the Nitric Oxide Gas expelled from the analysed Compound, Walter Crums method ("Journ. f. prakt. Chem.," 41, 201), 312 NITRIC ACID. [ 149. Fill a graduated tube, made of strong glass, about 30 centimetres long and 2 centimetres wide, with mercury, and invert in the trough. Put a weighed sample of the substance under examination (about Ol grm.) into a very small tube, which must be nearly filled by it, and paste gummed paper over the open end of the tube. Now introduce this into the mercurial tube, and add, by means of a pipette with curved point, somewhat less than a cubic centimetre of water, and then about 3 c.c. of sulphuric acid, and let it stand for about 2 hours, with occasional shaking, but without application of heat. After this, note the difference of the mercury column, and the state of the barometer and thermometer, as well as the height of the sulphuric acid, then add about 20 c.c. of a warm solution of sulphate of protoxide of iron, and let it stand for 3 or 4 hours, with occasional stirring. Read off again as before. The absorbed gas is nitric oxide, of which the specific gravity is 1*0399, and 1000 c.c. consequently weigh, at 32 F., and 29-8 Bar., 1-3509 grm. W. Crum obtained satisfactory results by this convenient method. d. Methods in which t/ie Nitrogen of the Nitrio Acid is separated and measured in the gaseous form. These methods are more particularly suitable for analysing nitrates which are decomposed by ignition into oxide or metal and oxides of nitrogen ; they will be found in the Section on the Ultimate Analysis of Organic Bodies, 185. Marignac ("Annal. de Chim. et de Phys.," 27, 315) employed them to analyse compounds of nitric acid with sub- oxide of mercury. Bromeis ("Annal. d. Chern. u. Pharm.," 72, 38), analysed nitrite, in cases where the choice is permitted (compare 102). 3. LIME FROM POTASSA AND SODA. Precipitate the lime with oxalate of ammonia ( 103, 2, b, a), filter, 14 evaporate the filtrate to dryness, and determine the alkalies in the ignited residue. In determining the alkalies, dissolve the residue, freed by ignition from the ammonia salts, in water, and filter the solution from the undissolved portion ; acidify the filtrate, according to circumstances, with hydrochloric acid or sulphuric acid, and then evaporate to dryness ; since oxalate of ammonia partially decomposes chlorides of the alkali metals upon ignition, and converts the bases into carbonates, except in presence of a large proportion of chloride of ammonium. The results are still more accurate than in A, ex- * This operation effects also the removal of the sraall quantity of sulphuric acid added to precipitate the traces of baryta, as sulphates of the alkalies are converted into chlo- rides of the alkali inetals upon ignition in presence of a large proportion of chloride of ammonium. II. Y 322 SEPARATION OF THE BASES. [ 153. cept where oxalate of ammonia has been used, after the precipitation by carbonate of ammonia, to remove the minute traces of lime from the filtrate. 4. MAGNESIA FROM POTASSA AND SODA. a. Methods based upon the sparing solubility of Magnesia in Water. a. Make a solution of the bases, as neutral as possible, and free 15 from ammonia salts (whether the acid is sulphuric acid, hydrochloric acid, or nitric acid, is indifferent), add baryta-water as long as a pre- cipitate forms, heat to boiling, filter the fluid off from the precipitate, and wash the latter with boiling water. The precipitate contains the magnesia as hydrate ; the magnesia is determined either as directed in 104, 1, b, or the precipitate is dissolved in hydrochloric acid, the baryta thrown down with sulphuric acid, and the magnesia as phosphate of magnesia and ammonia (104, 2). The alkalies, which are contained in the solution, according to circumstances, as chlorides, nitrates, or caustic alkalies, are separated from the baryta as directed in 10 or 12- Liebig, who was the first to employ this method, proposes crystallized sulphide of barium as precipitant. The method gives good results, but is rather tedious. /3. Precipitate the solution with a little pure milk of lime, boil, 1Q filter, and wash. Separate the lime and the magnesia in the preci- pitate as directed 154 ; the lime and the alkalies in the filtrate, as directed in 10 or 14- This method is advantageoxisly employed in cases where it is desirable to remove the magnesia from a fluid con- taining lime and alkalies, which latter alone it is intended to determine. y. Evaporate the solution of the chlorides (which must contain no 17 other acids) to dryness, and, if chloride of ammonium is present, ignite ; warm the residue with a little water ; this will dissolve it with the exception of some magnesia, which separates. Add to the solution elutriated oxide of mercury, evaporate to dryness on the water-bath, with frequent stirring, and proceed exactly as directed 104, 3, 6. There is no need to continue the ignition until the whole of the oxide of mercury is expelled ; on the contrary, part of it may be filtered off together with the magnesia, and subsequently volatilized upon the ignition of the latter. The solution contains the alkalies in form of chlorides (Berzelius). This method gives satis- factory results. Take care to add the oxide of mercury only in proper quantity, and always test the solution of the alkaline chlorides for magnesia, of which it will generally be found to retain a trace. <5. Add to the solution of the chlorides oxalic acid in sufficient 18 quantity to convert all the bases present, viewed as potassa, into quadroxalate ; add some water, evaporate to dryness, in a platinum dish, and ignite. By this operation the chlorides of the alkali metals are partially, the chloride of magnesium completely, converted into oxalates, which, upon ignition, give carbonated alkalies and magnesia. The salts of the alkalies are separated from the magnesia by boiling water. If the solution looks a little turbid, evaporate to dryness, treat the residue with water, and filter off the trifling amount of magnesia still remaining ; add, finally, hydrochloric acid to the filtrate, and determine the alkalies as chlorides. 153.] SEPAEATION OF THE BASES. 323 If the bases are present in form of sulphates, add to the boiling 19 solution chloride of barium, until the formation of a precipitate just ceases, evaporate the filtrate with an excess of oxalic acid, and proceed as in 18- Separate the undissolved carbonate of baryta, which remains mixed with the magnesia, from the latter as directed 154. We owe these methods to Mitscherlich ; they have recently been described by Lasch (" Journ. f. prakt. Chem.," 63, 343). I can add my own testimony to the accuracy of the results. I cannot recommend /Sonnenschein's method (boiling the chlorides with carbonate of oxide of silver), as the filtrate invariably retains more than mere traces of magnesia. The method described in 18, may also be successfully employed with nitrates, for which it is, indeed, specially recommended by Deville (" Journ. f. prakt. Chem.," 60, 17). Carbonic acid and nitrous acid gas are evolved in the process of evaporation. b. Method based upon tlie Precipitation of Magnesia by Phosphate of Ammonia or Ar senate of Ammonia. Add to the solution containing magnesia, potassa, and soda, am- 21 monia in excess, and some chloride of ammonium, should this not be present already ; precipitate the magnesia with a slight excess of pure phosphate of ammonia. Filter, remove the free ammonia from the nitrate by evaporation, and then precipitate the phosphoric acid with acetate of lead as a combination of phosphate of lead and chloride of lead. Remove the excess of oxide of lead from the still hot fluid by ammonia and carbonate of ammonia, filter, and determine the potassa and soda in the filtrate as directed 97 and 98. (0. L. Erdmann, "Journ. f. prakt. Chem.," 41, 89; Heintz, "Pogg. Annal.," 73, 1 1 9). I cannot concede the preference to this method over those given in a. The following process is much more simple : 22 precipitate the magnesia with arseuate of ammonia, instead of phos- phate, and estimate it as arsenate of magnesia as directed 127, 2. Evaporate the filtrate to dryness, and heat the residue in a porcelain crucible. Should the mass not have contained sufficient chloride of ammonium, add some of the latter substance to the residue, and then ignite again. As this operation effects the ready and complete volatilization of the arsenic acid, the alkalies are left behind as pure chlorides. I need hardly mention that proper arrangements to secure the safe removal of the arsenical furnes are indispensable. C. v. Hauer (" Jahrbuch d. K. K. geolog. Keichsanst.," Jahrgang IV., 863) recommends a similar method. c. Indirect Met/tod, which gives also, at the same time, the quantity of Potassa and Soda, if both are present. Convert, with proper care, the bases into pure neutral sulphates, 23 weigh, dissolve in water, and determine the sulphuric acid by chloride of barium ( 132) ; filter, precipitate the excess of baryta from the filtrate by sulphuric acid, filter again, concentrate the filtrate by evaporation, and determine the magnesia as directed 104, 2 (K. List, " AnnaL d. Chem. u. Pharm.," 81, 117). Calculate the magnesia found as sulphate, and deduct the resulting 24 weight from the total weight of the sulphates: the difference shows the quantity of the sulphated alkalies ; deduct also the SAilphuric Y2 824 SEPARATION OP THE BASES. [ 154. acid combined with the magnesia from the total quantity of sul- phuric acid : the difference gives the amount of sulphuric acid com- bined with the alkalies. See 152, 3 (6). II. SEPARATION OP THE OXIDES OF THE SECOND GROUP FROM EACH OTHER. 154. Index : Baryta from strontia, 26, 29 ; from lime, 26, 28, 29 j from magnesia, 25, 27. Strontia from baryta, 26, 29 ; from lime, 32, 33 ; from magnesia, 25. Lime from baryta, 26, 28, 29 ; from strontia, 32, 33 ; from magnesia, 25, 30, 31. Magnesia from baryta, 25, 27 ; from strontia, 25 ; from lime, 25, 30, 31. A. General Method. THE WHOLE OF THE ALKALINE EARTHS FROM EACH OTHER. Proceed as in 10. The magnesia is precipitated from the 25 filtrate with phosphate of soda. The precipitated carbonates of the baryta, strontia, and lime, are dissolved in hydrochloric acid, and the bases separated as directed in 26- B. Special Methods. 1. Method based upon the Insolubility of Silicofluori.de of Barium. BARYTA FROM STRONTIA AND FROM LIME. Mix the neutral or slightly acid solution with hydrofluosilicicacid 26 in excess, add a volume of spirit of wine equal or somewhat inferior to that of the fluid (H. Rose), let the mixture stand 12 hours, filter the precipitate of silicofluoride of barium on a weighed filter, wash with a mixture of equal parts of water and spirit of wine, until the washings cease to show even the least trace of acid reaction (but no longer), and dry at 212F. Precipitate the strontia or lime from the filtrate by dihrte sulphuric acid ( 102, 1 a, and 103, 1). The results are satisfactory. For the properties of silicofluoride of barium, see 71. If both strontia and lime are present, the sul- phates are weighed, converted into carbonates ( 132, II., b), and the two bases then separated as directed in 32 or 33- 2. Methods based upon the Insolubility of Sulphate of Baryta. a. BARYTA FROM MAGNESIA. Precipitate the baryta with sulphuric acid ( 101, 1, a.), and the 27 magnesia from the nitrate with phosphate of soda and ammonia ( 104, 2). b. BARYTA FROM LIME. Mix the solution with hydrochloric acid, then with highly dilute 28 sulphuric acid (1 part acid to 300 water), as long as a precipitate forms ; let deposit, and determine the sulphate of baryta as directed iu 101, 1, a. Add to the filtrate the washings, concentrated pre- 154.] SEPARATION OF THE BASES. 323 viously by evaporation, neutralize the acid with ammonia, and pre- cipitate the liine as oxalate ( 103, 2, b, a). The results are ac- curate. 3. Method based upon the different deportment with Carbonated Alkalies of Sulphate of Baryta on the one, and Sulphates of Strontia and Lime on the ot/ter hand. BARYTA FROM STRONTIA AND LIME. Digest the precipitated sulphates of the three bases for 12 hours, 29 at the common temperature, with frequent stirring, with a solution of carbonate of ammonia, decant the fluid on to a filter, treat the undissolved residue repeatedly in the same way, wash finally with water, and separate the undecomposed sulphate of baryta by means of dilute hydrochloric acid from the carbonate of strontia and lime formed (H. Rose, "Pogg. Annal.," X.GV. 286, 299, 427). 4. Methods based upon the Insolubility of Oxalate of Lime in Chloride of Ammonium and in Acetic Acid. LIME FROM MAGNESIA. a. Mix the properly diluted solution with sufficient chloride of 30 ammonium to prevent the formation of a pi*ecipitate by ammonia, which is added in very slight excess ; add oxalate of ammonia as long as a precipitate forms, then a further portion of the same re-agent, about sufficient to convert the magnesia also into oxalate (which remains in solution). This excess is absolutely indispensable to ensure complete precipitation of the lime, as oxalate of lime is slightly soluble in solution of chloride of magnesium not mixed with oxalate of ammonia (Analytical Notes and Experiments, No. 89). Let the mixture stand 12 hours in a moderately warm place, remove the supei'natant clear fluid, as far as practicable, from the precipi- tated oxalate of lime, mixed with a little oxalate of magnesia, by decanting on to filter, wash the precipitate once more in the same way by decantation, then dissolve in hydrochloric acid, add ammonia in slight excess, and oxalate of ammonia. Let the fluid stand until the precipitate has completely subsided, then pour on to a filter, transfer the precipitate finally to the latter, and proceed exactly as directed 103, 2, b, a. The first filtrate contains the larger portion of the magnesia, the second the remainder. Evaporate the second filtrate, acidified with hydrochloric acid, to a small volume, then mix the two fluids, and precipitate the magnesia with phosphate of soda as directed in 104, 2. If the quantity of ammonia salts present is considerable, the estimation of the magnesia is rendered more accurate by evaporating the fluids, in a large platinum or silver dish,* to dryness and igniting the residuary saline mass, divided in several portions, in a smaller platinum dish, until the ammonia salts are expelled. The residue is then treated with hydrochloric acid and water, heat applied, the fluid filtered? and the filtrate finally precipitated with ammonia and phosphate of soda. * A porcelain dish does not answer so well (see Analytical Notes and Experiments, No. 3). t If the process of evaporation has been conducted in a silver vessel, a little chloride of silver will often separate. 326 SEPARATION OF THE BASES. [ 155. Numerous experiments recently made in my laboratory have con- vinced me that this method, which is so frequently employed, gives accurate results only if the foregoing instructions are strictly complied with. It is only in cases where the quantity of magnesia present is relatively small, that one single precipitation with oxalate of am- monia may be found sufficient (comp. Anal. Notes and Experim., No. 90). b. In the case of lime and magnesia combined with phosphoric 31 acid, dissolve in the least possible quantity of hydrochloric acid, add ammonia until a copious precipitate forms; redissolve this by addition of acetic acid, and precipitate from the solution the lime with an excess of oxalate of ammonia. As free acetic acid by no means prevents the precipitation of small quantities of oxalate of magnesia, the precipitate contains some magnesia, and, as oxalate of lime is not quite insoluble in acetic acid, the nitrate contains some lime, which two sources of error compensate each other in some measure. In accurate analyses, however, these trifling admixtures of magnesia and lime are afterwards separated from the weighed precipitates of car- bonate of lime and pyrophosphate of magnesia. 5. Method based upon the Insolubility of Nitrate of Sirontia in Alcohol. STRONTIA FROM LIME. Treat the nitrates with absolute alcohol. Filter the fluid from the 32 undissolved nitrate of strontia, wash with alcohol, dissolve in water, and determine as sulphate of stroutia ( 102, 1). Precipitate the lime from the filtrate by sulphuric acid. The results are approximate. This method is applicable only where the proportion of lime is large, that of strontia small. 6. Indirect Method. STRONTIA AND LIME. Determine both bases first as carbonates, precipitating them either 33 with carbonate or with oxalate of ammonia ( 102 and 103); then estimate the amount of carbonic acid in them by fusion with fused borax ( 139, II., d), and from the results calculate the amount of strontia and lime as directed in 200. This method gives very accurate results, except either of the two bases be present in very small proportion only. THIRD GROUP. ALUMINA SESQUIOXIDE OF CHROMIUM. I. SEPARATION OF THE OXIDES OF THE THIRD GROUP FROM THE ALKALIES. 155. 1. FROM AMMONIA. a. Salts of alumina and of sesquioxide of chromium may be sepa- 34 rated from salts of ammonia by ignition. However, in the case of alumina, this method is applicable only in the absence of chlorine (volatilization of chloride of aluminium). The safest way, therefore, is to mix the compound first with carbonate of soda, and ignite after. 6. Determine the ammonia by one of the methods given in 99, 3, 35 156.] SEPARATION OF THE BASES. 327 using solution of potassa or soda to effect the expulsion of the ammonia. The alumina and sesquioxide of chromium are then determined in the residue in the same way as in 36* 2. FROM POTASSA AND SODA. a. Precipitate and determine the sesquioxide of chromium and 36 alumina as directed in 105, a, and 106, a. The nitrate contains the alkalies, which are then freed from the salt of ammonia formed, by evaporation to dryness and ignition. b. Alumina may be separated also from potassa and soda, by heating 37 the nitrates of the three bases (see 39)- II. SEPARATION OP THE OXIDES OF THE THIRD GROUP FROM THE ALKALINE EARTHS. 156. Index: 1. Alumina from baryta 38, 39, 40, 41, 42, 43; from strontia 38, 39, 40, 41, 42, 43; from lime, 38, 39, 40, 41, 42, 44, 45, 46; from magnesia, 38, 39, 40, 41, 42, 45, 46. 2. Sesquioxide of Chromium from the alkaline earths, 47, 48. 1. SEPARATION OF ALUMINA FROM THE ALKALINE EARTHS. A. General Methods. THE WHOLE OF THE ALKALINE EARTHS FROM ALUMINA. 1. Method based upon the Precipitation of Alumina by Ammonia, and iipon its Solubility in Solution of Soda. Mix the hot solution, in a beaker, with chloride of ammonium, 38 add a slight excess of ammonia, free from carbonic acid, place the beaker on a flat stoneware plate filled with ammoniated water, and invert over it a larger beaker, with the rim dipping into the ammoniacal fluid, by which means the carbonic acid of the atmo- sphere is effectively excluded. After 12 hours, decant, and then wash the hydrate of alumina exactly as directed 105, a. The solution contains the baryta, strontia, and lime, with the greater part of the magnesia, the remainder of the' latter being with the hydrate of alumina in a kind of chemical combination. The preci- pitate often contains, notwithstanding every precaution used to avoid it, also minute quantities of carbonate of baryta, strontia, and lime. Dissolve the hydrate of alumina in hydrochloric acid, by transferring it with a spatula, as far as practicable, to a platinum or porcelain dish, treating the filter with warm hydrochloric acid, to extract the last adhering particles of the hydrate, and employing the hydrochloric acid running off, to effect the solution of the precipitate in the dish; concentrate the fluid by evaporation, add pure solution of soda or potassa or, better still, pure solid hydrate of potassa or soda, until the precipitate of hydrate of alumina formed is redissolved ; heat, filter off hot from the hydrate of magnesia which separates, wash the latter carefully with hot water, dissolve in some hydrochloric acid, mix with ammonia in excess, and add the clear solution to the filtrate of the first operation, which contains the larger portion of the mag- nesia; if the solution is not perfectly clear, filter off from the trifling 328 SEPARATION OF THE BASES. [ 156. deposit of alumina, and add the filtrate to that of the first operation. It will be seen that in this way the minute quantities of carbonate of baryta, strontia, and lime, which have precipitated with the hydrate of alumina, are restored to the bulk of the substances in that filtrate. The further separation of the alkaline earths is effected by evaporat- ing the fluid, acidified with hydrochloric acid, in a platinum dish, or in a glass flask, and adding to the concentrated warm fluid ammonia in slight excess. This usually produces a trifling precipitate of alumina, which is filtered off, washed, and weighed together with the principal precipitate. The alkaline earths are determined iu the filtrate as directed 154. The alumina is precipitated from the alkaline solution by strongly acidifying with hydrochloric acid, boil- ing with some chlorate of potassa (to destroy the traces of organic matter which the solution of soda or potassa may have dissolved out of the filter paper, and which would interfere with the precipitation of the alumina), and then adding ammonia ( 105, a). If all that is required is to separate alumina from baryta, strontia, or lime, and the amount of the latter bodies is relatively large, it is often the best way to redissolve the tolerably well- washed alumina precipitate in hydrochloric acid, heat the solution for a considerable time, and then precipitate again with ammonia. By this course of proceeding the alumina is obtained perfectly free from alkaline earths. 2. Metliod based upon the unequal Decomposabillty of the Nitrates at a Moderate Heat (Deville, " Journ. f. prakt. Chem.," 1853, 60, 9). To make this simple and convenient method applicable, the bases 39 must be present as pure nitrates. Evaporate to dryness in a covered platinum dish, and heat gradually in the sand or air-bath (or, better still, on a cylindrical iron plate similar to that described in 31 see Fig. 36 with two cavities, one for the platinum dish, the other, filled with brass filings, for the thermometer) to about 392 482 F., until a glass rod moistened with ammonia ceases to indicate further evolution of nitric acid fumes. You may also, with- out risk, continue to heat until nitrous acid vapors form. The residue consists of alumina, nitrates of baryta, strontia, and lime, nitrate and basic nitrate of magnesia. Moisten the mass with a concentrated solution of nitrate of am- monia, and heat gently, but do not evaporate to dryness. Repeat this operation until no further evolution of ammonia is perceptible. (The basic nitrate of magnesia, insoluble in water, dissolves in nitrate of ammonia, with evolution of ammonia, as neutral nitrate of magnesia.) Add water, and digest at a gentle heat. If the nitrate of ammonia has liberated only imperceptible traces of ammonia, pour hot water into the dish, stir, and add a drop of dilute ammonia ; this must cause no turbidity iu the fluid ; should the fluid become turbid, this proves that the heating of the nitrates has not been continued long enough ; in which case you must again evaporate the contents of the dish, and heat once more. The alumina remains uudissolved in the form of a dense granular substance. Decant after digestion, and wash with boiling water ; ignite strongly in the same vessel in which the separation has been 156.] SEPARATION OP THE BASES. 329 effected, and weigh. Separate the alkaline earths as directed 154. In the same way alumina may be separated also from potassa and soda. 3. Method in which the processes of 1 and 2 are combined. Precipitate the alumina as in 38> wash in the same way as there 40 directed, then treat with nitric acid, and proceed according to the directions of 39j to remove the trifling amount of magnesia, d. The results are satisfactory. 41 5. Method based upon the Formation of a Soluble Alkaline Alu- minate in the dry way. See 100 ( 161). 42 B. Special Methods. SOME OF THE ALKALINE EARTHS FROM ALUMINA. 1. Method based upon the Precipitation of some oftlte Salts of the Alkaline EartJis. a. BARYTA AND STRONTIA FROM ALUMINA. Precipitate the baryta and strontia with sulphuric add ( 101 43 and 102), and the alumina from the filtrate as directed 1 2). This method, which was formerly much employed, may be resorted to also to effect the joint separation of both lime and magnesia from alumina ; but satisfactory results can only be expected if the quan- tity of lime is very small. In cases of the kind, the fluid must be largely diluted before the bicarbonate of soda is added, and the pre- cipitation must be effected in a stoppered flask. The precipitate of alumina is apt to retain some lime and magnesia. b. ALUMINA FROM MAGNESIA, AND SMALL QUANTITIES OF LIME. Mix the slightly acid dilute fluid, in a stoppered flask, with elutri- 46 ated carbonate of baryta, in moderate excess ; let the mixture stand in the cold until the hydrated alumina has completely subsided, wash by decantatiou three times, and then determine the alumina in the precipitate as directed 43 ; the magnesia and lime in the fil- trate as directed in 154, after previous removal of the baryta by sulphuric acid, according to the directions of 28- " 2. SEPARATION OF SESQUIOXIDE OF CHROMIUM FROM THE ALKA- LINE EARTHS. The best way to effect the separation of sesquioxide of chromium 47 from all the alkaline earths at the same time, is to convert the sesqui- oxide into chromic acid. For this purpose the pulverized substance is mixed with 2^ parts of pure carbonate of soda and 2^ parts of nitrate of potassa, and the mixture heated in a platinum crucible to fusion. On treating the fused mass with hot water, the chromium dissolves as alkaline chromate ; the residue contains the alkaline earths as carbonates, or in the caustic state (magnesia). The chro- mium in the solution is determined as directed 130. I need hardly observe that sesquioxide of chromium may also be 48 separated from baryta and, though less perfectly, from strontia, by means of sulphuric acid added to the acid solution of the substance. Sesquioxide of chromium cannot be separated by ammonia from the alkaline earths, since, even though carbonic acid be completely ex- cluded, particles of the alkaline earths are thrown down with the sesquioxide of chromium. From solutions containing a salt of ses- quioxide of chromium, lime cannot be precipitated completely by oxalate of ammonia ; but it may be by sulphuric acid and alcohol ( 103, 1). III. SEPARATION OF SESQUIOXIDE OF CHROMIUM FROM ALUMINA. 157. Fuse the oxide with two parts by weight of nitrate of potassa and 49 4 parts of carbonate of soda, in a platinum crucible, treat the fused mass with boiling water, rinse the contents of the crucible into a porcelain dish or beaker, add a somewhat large quantity of chlorate of potassa, supersaturate slightly with hydrochloric acid, evaporate to the consistence of syrup, and add, during the latter process, some more chlorate of potassa in portions, to remove the free hydrochloric acid. Dilute now with water, and precipitate the alumina by am- monia or carbonate of ammonia as directed in 105, a. The alumina falls down free from sesquioxide of chromium. The chromium in 158.] SEPARATION OP THE BASES. 831 the filtrate is determined as directed 130. If you omit the evapo- ration with hydrochloric acid and chlorate of potassa, part of the chromic will be reduced by the nitrous acid in the fluid, and sesqui- oxide of chromium will accordingly, upon addition of ammonia, pre- cipitate with alumina (Dexter, " Pogg. Annal.," 89, 142). FOURTH GROUP. OXIDE OF ZINC PROTOXIDE OF MANGANESE PROTOXIDE OF NICKEL PROTOXIDE OF COBALT PROTOXIDE OF IRON SESQUIOXIDE OF IRON. I. SEPARATION OF THE OXIDES OF THE FOURTH GROUP FROM THE ALKALIES. 158. A. General Methods. 1. ALL THE OXIDES OF THE FOURTH GROUP FROM AMMONIA. Proceed as for the separation of sesquioxide of chromium and 50 alumina from ammonia (34, 155). It must be borne in mind that the oxides of the fourth group comport themselves, upon ignition with chloride of ammonium, as follows : Sesquioxide of iron is partly volatilized as sesquichloride ; the oxides of manganese are converted into protochloride of manganese, containing protosesqui- oxide of that metal ; the oxides of nickel and cobalt are reduced to the metallic state ; oxide of zinc volatilizes, with access of air, as chloride of zinc (H. Rose). It is, therefore, generally the safest way to add carbonate of soda. The ammonia is determined in a separate portion. 2. ALL OXIDES OF THE FOURTH GROUP FROM POTASSA AND SODA. Mix with ammonia until the fluid is neutral, add sulphide of am- 51 inonium, and filter off the sulphides from the fluid containing the alkalies. The precautionary measures recommended in the case of sulphide of nickel ( 110, 6), must be carefully attended to. other- wise part of that sulphide will remain in solution. Acidify the filtrate with hydrochloric acid, concentrate by evaporation, filter from, the sulphur, evaporate the filtrate to dryuess, ignite the residue, to effect the removal of the ammonia salts, and determine the alkalies by the methods given in 152. Nickel and cobalt may be separated from the alkalies also by the method given 170, B, 2, 6 (67). B. Special Methods. 1. OXIDE OF ZINC FROM POTASSA AND SODA, by precipitating 52 the zinc from the solution of the acetate with sulphuretted hydrogen (see 66)- 2. PROTOXIDE OF NICKEL AND PROTOXIDE OF COBALT FROM THE ALKALIES, by igniting the chlorides in a stream of hydrogen gas (see 72). 3. SESQUIOXIDE OF IRON FROM POTASSA AND SODA, by precipitat- ing the sesquioxide of iron with ammonia ; or by heating the nitrates (see 39). 4. PROTOXIDE OF MANGANESE FROM THE ALKALIES. a. Saturate the solution with cldorine, and precipitate the 53 332 SEPARATION OP THE BASES. [ 159. manganese as hydrated sesquioxide with carbonate of baryta or ammonia. The latter precipitant is apt to leave some manganese in solution. b. Precipitate the manganese with peroxide of lead (Gibbs) ; (see 58)- The acid with which the bases are combined may be hydrochloric acid, nitric acid, or sulphuric acid. If the choice is allowed, select the first. c. Heat the nitrates (Deville) ; (see 58 y). II. SEPARATION OF THE OXIDES OF THE FOURTH GROUP FROM THE ALKALINE EARTHS. 159. Index : Oxide of zinc from baryta and strontia, 54, 55, 56, 60 ; from lime, 54, 56, 60 ; from magnesia, 54, 56. Protoxide of manganese from baryta and strontia, 54, 55, 58,59; from lime and magnesia, 54, 58, 59. Protoxides of nickel and cobalt from baryta and strontia, 54,55,60,61; from lime, 54, 60, 6 ! ; from magnesia, 54,61. Sesquioxide of iron from baryta and strontia, 54, 55, 57 ; from lime and magnesia, 54, 57. A. General Method. ALL OXIDES OF THE FOURTH GROUP FROM THE ALKALINE EARTHS. 54. Add to the solution, in a flask with stopper, chloride of ammonium and, if acid, also ammonia, and precipitate with sulphide of ammo- nium, as in 51- Take care to use slightly yellow sulphide of ammonium, perfectly saturated with sulphuretted hydrogen, and free from car- bonate and sulphate of ammonia, and to employ it in sufficient excess. Insert the stopper, and let the flask stand for some time, to allow the precipitate to subside, then wash quickly, and as far as practicable, o\it of the contact of air, with water to which some sulphide of ammo- nium has been added. Acidify the filtrate with hydrochloric acid, heat, filter from the sulphur, and separate the alkaline earths, as directed in 1 54. If the quantity of the alkaline earths is rather considerable, it is advisable to treat the precipitate once more with hydrochloric acid, heat the solution gently for some time, and then re-precipitate in the same way. In presence of nickel and cobalt, it is not necessary to effect complete solution. These two latter metals may be separated also from the alkaline earths by the method given 170, B, 2, b (67)- B. Special Methods. 1. BARYTA AND STRONTIA FROM THE WHOLE OF THE OXIDES OF THE FOURTH GROUP. Precipitate the baryta and strontia from the acid solution with 55 sulphuric acid (101 and 102). This method is preferable to any other to effect the separation of baryta from the oxides of the fourth group. 2. OXIDE OF ZINC FROM THE ALKALINE EARTHS. Convert the bases into acetates, and precipitate the zinc from 56 the solution as directed in 108, b. 3. SESQUIOXIDE OF IRON FROM THE ALKALINE EARTHS. 159.] SEPARATION OF THE BASES. 333 a. Precipitate the dilute solution with bicarbonate of soda or 57 with carbonate of baryta (see 45, 46). b. Precipitate the sesquioxide of iron with succinate of am- monia ( 113, 1, c). c. Decompose the nitrates by heat (39)- d. Add carbonate of soda to the moderately dilute solution, until the fluid is nearly neutral and has acquired a deep brownish-red tint ; add acetate of soda, boil for some time, c i f wash three times by boiling, and then filter off the brown- ish-red precipitate, which contains all the sesquioxide of iron in form of a basic salt. Wash with boiling water to which some acetate of ammonia has been added. The thoroughly washed sequioxide of iron may either be dried, ignited, and weighed ; or dissolved, whilst still moist, in hydrochloric acid, and the solution precipitated with ammo- nia ( 113, 1 c). If you wish to avoid the use of fixed alkalies, you may substitute carbonate and acetate of ammo- nia for the corresponding soda salts. The results are satis- factory. e. Precipitate with ammonia, conducting the operation exactly as directed 38- If you wish to employ this method in presence of rather large quantities of iron and magnesia, you must re-dissolve in hydrochloric acid the hydra ted sesquioxide of iron containing magnesia, and precipitate with bicarbonate of soda. With small quanti- ties of iron, it is generally sufficient to re-dissolve the pre- cipitate in hydrochloric acid, and precipitate again with ammonia. 4. PROTOXIDE OF MANGANESE FROM THE ALKALINE EARTHS. a. Methods based upon the separation of Manganese as Sesquioxide or Binoxide. a. Gibbs's Method (" Annal. der Chem. und Pharm ," 86, 54). Add 58 to the perfectly neutral solution of the bases, which may be combined with hydrochloric acid or nitric acid,* or, in the case of magnesia, with sulphuric acid, pure binoxide of lead.f in the proportion of 5 grammes of the binoxide to 1 gramme of substance ; digest for an hour at about 185 F., with frequent stirring, filter the fluid from the precipitate, which contains the whole of the manganese, probably as sesqnioxide, and wash with boiling water. If magnesia is present, let the digested fluid cool, then add a few drops of nitric acid before proceeding to nitration. Determine the alkaline earths (and alkalies) in the filtrate as directed in 152 and 154. Ignite the precipitate, dissolve in strong nitric acid, and separate the manganese and lead as directed in 162. This method is a little complicated. Presence of free hydrochloric acid does not interfere with the process, but free nitric acid and sulphuric must not be present; compare Will, " Annal. der Chem. und Pharm.," 86, 62. * Hydrochloric acid deserves the preference if, besides the alkaline earths, alkalies are present ; if not, nitric acid is preferable. t The biaoxide of lead prepared from minium is not adapted for use in this process, on account of the impurities which it contains. Pure biuoxide may be obtained by treating the hydrated oxide diffused in water, with chlorine, washing the product with boiling water, digesting with nitric acid, and washing. 334 SEPARATION OF THE BASES. [ 159. /3. Schiefs Method (Sillim. Journal, 15, 275). Add to the hydro- chloric acid solution carbonate of soda until the fluid is nearly neutralized, mix with acetate of soda, and then conduct chlorine gas into the mixture. The acetate of protoxide of manganese is decora- posed, and the whole of the manganese separates as binoxide. The alkaline earths remain in solution. Experiments made by Rivot, Beudant and Daguin, and also in my laboratory, have shown that an acetic or nitric acid solution answers better than one in hydro- chloric acid. The acetic or nitric acid solution is kept heated to between 122 and 140 F., whilst the chlorine gas is transmitted through it ; as soon as the binoxide has separated, the transmission of the gas is stopped. In an experiment made by me, I found that the protosesqui oxide of manganese obtained by the ignition of the binoxide so produced contained alkali. The binoxide must there- fore be dissolved in hydrochloric acid, and the solution precipitated as directed 109, 1, a. Instead of chlorine gas, solution of hypochlo- rous acid or of hypochlorite of soda may be used. In using the latter, care must be taken to keep the fluid always slightly acid by acetic acid. The method is good. y. Devilles Method (" Journ. f. prakt. Chern.," 60, 11). The bases must be present as nitrates. Heat in a covered platinum dish to from 392 to 482 F., until the formation of fumes has completely ceased, and the mass has become black ; and proceed in all other respects as directed in 39- The presence of a small quantity of or- ganic matter, or the action of a too intense heat, may cause the reduc- tion of traces of binoxide of manganese, and their solution in nitrate of ammonia ; these traces will be found with the magnesia. & Saturate the solution with chlorine gas, or, if the quantity of manganese is very minute, with chlorine water, and precipitate the manganese as hydrated oxide, with bicarbonate of soda or carbonate of baryta (H. Rose). Before weighing the protosesquioxide of manga- nese, you must make quite sure that it contains no admixture of alkali (see /3). b. Methods based upon the Volumetric Determination of Man- ganese, according to Bunsen and Krieger (" Annal. der Chem. und Pharm.," 87, 268). a. MANGANESE FROM MAGNESIA. Precipitate with solution of soda ( 109, 1, 5). Wash the precipi- 59 tate thoroughly, ignite, and weigh. If the quantity of magnesia pre- sent is suflicient, the residue has the formula, Mn a O s , MgO + zMgO. Treat a weighed sample of it as directed in 142, towards the end ; this will give the quantity of the manganese (1 equivalent of chlorine, or of liberated iodine, corresponds to 1 equivalent of Mn 2 O 3 ) ; from the difference you may calculate the quantity of the magnesia. ft. FROM BARYTA AND STRONTIA. Precipitate with carbonate of soda ( 109, 1, a). The ignited pre- cipitate has the formula, Mn a 8 , Ba + x Ba O, O s . 159.] SEPARATION OF THE BASES. 335 Treat a sample as in a ; this will give the quantity of the manganese. To find that of the carbonate of baryta, deduct the weight of the ses- quioxide of manganese from that of the weighed precipitate, and add to the difference so much carbonic acid as has been expelled by the sesquioxide of manganese, that is, for each equivalent of Mn z O^ an equivalent of C O 2 . y. FROM LIME. Proceed as in ft ; but after ignition, moisten the residue with car- bonate of ammonia, evaporate again to dryness, and ignite gently, and repeat the same operation until the weight remains constant. In the case of lime it is better to ignite the precipitate over the blast gas-lamp until the lime is reduced to the caustic state. N.B. This method of volumetric determination of manganese presupposes the presence of more than 1 equivalent of MgO, CaO, &c., to 1 equivalent of Mn 2 O s ; for if the case is different, the residue contains, besides Mn, O 3 , also Mn 2 O $ , Mn 0. To adapt the method also to cases of the latter description, Krieger recommends the follow- ing process : dissolve a sample of the weighed precipitate, add half the weight of oxide of zinc, precipitate with carbonate of soda, ignite the precipitate some time in the air, determine the quantity of the residue, and use the latter or an aliquot part of it, for the volumetric determination. This residue contains the whole of the manganese as Mn 2 O s . 5. PROTOXIDE OF COBALT, PROTOXIDE OF NICKEL, AND OXIDE OF ZINC, FROM BARYTA, STRONTIA, AND LIME. Mix with carbonate of soda in excess, add cyanide of potassixim, 60 heat very gently, until the precipitated carbonates of protoxide of cobalt, protoxide of nickel, and oxide of zinc are redissolved ; then filter the cyanide of potassium solution of the metallic cyanides off from the carbonated alkaline earths. Dissolve the 'latter in dilute hydrochloric acid, and separate them as directed in 154. Separate the metals as directed 160. 6. PROTOXIDE OF COBALT AND PROTOXIDE OF NICKEL FROM MAG- NESIA. Precipitate with a mixture of solution of hypochlorite of potassa 61 and solution of caustic potassa. The precipitate consists of peroxide of nickel, sesquioxide of cobalt, and hydrate of magnesia ; wash thoroughly, and digest, whilst still moist, at a temperature of from 86 to 104 F., with an excess of solution of chloride of mercury. In this process, a double salt is formed of Mg Cl + 3 Hg Cl, and the magnesia is dissolved, whilst a corresponding quantity of basic chlo- ride of mercury precipitates (Ullgren, BerzeL, " Jahresber.," 21, 146). Evaporate the solution and washings, with addition of pure oxide of mercury, and determine the magnesia as directed? 104, 3, b. Remove the mercury from the oxides of nickel and cobalt by ignition, and separate the two metals as directed below. 7. PROTOXIDE OF COBALT AND PROTOXIDE OF NICKEL FROM BARYTA, STRONTIA, AND LIME. Ignite the chlorides of the metals in hydrogen gas (72)- 336 SEPARATION OF THE BASES. [ 160. III. SEPARATION OF THE OXIDES OF THE FOURTH GROUP FROM THOSE OF THE THIRD, AND FROM EACH OTHER. 160. Index : Alumina from oxide of zinc, 62, 63, 66, 80, 83 ; from prot- oxide of manganese, 62, 63, 64, 74, 75, 80, 92 ; from prot- oxide of nickel, 62, 63, 65, 83 ; from protoxide of cobalt, .62, 63, 65, 83 ; from protoxide of iron, 62, 63, 64, 65 j from ses- quioxide of iron, 63, 64, 65, 69, 90. Sesquioxide of chromium from oxide of zinc, protoxide of manganese, protoxide of nickel, protoxide of cobalt, and protoxide of iron, 62, 63, 73 ; from sesquioxide of iron, 63, 69, 73. Oxide of zinc from alumina, 62, 63, 66, 80, 83; from sesqui- oxide of chromium, 62, 73 ; from protoxide of manganese, 66, 74, 75, 93 ; from protoxide of nickel, 66, 68, 71, 87, 88; from protoxide of cobalt, 66, 68, 71, 85, 88 ; from sesquioxide of iron, 62, 66, 77, 80,89, 91. Protoxide of manganese from alumina, 62, 63, 64, 74, 75, 80, 92 ; from sesquioxide of chromium, 62, 63, 73 ; fro^na oxide of zinc, 66, 74, 75, 93 ; from protoxide of nickel, 67, 68, 72. 74, 75, 76 ; from protoxide of cobalt, 67, 68, 72, 86 ; from sesqui- oxide of iron, 62, 77, 78, 80, 92. Protoxide of nickel from alumina, 62, 63, 65, 83 : from ses- quioxide of chromium, 62, 63, 73 ; from oxide of zinc, 66, 68, 71, 82, 87, 88 ; from protoxide of manganese, 67, 68, 72, 74, 75, 76, 82 ; from protoxide of cobalt, 76, 82, 84 ; from ses- quioxide of iron, 62, 67, 77, 78, 91. Protoxide of cobalt from alumina, 62, 63, 65, 83 ; from ses- quioxide of chromium, 62, 63, 73 ; from oxide of zinc, 66, 68, 71, 82, 85, 88 ; from protoxide of manganese, 67, 68, 72, 82, 86 ; from protoxide of nickel, 76, 82, 84 ; from sesquioxide of iron, 62, 67,77, 81. Protoxide of iron from alumina, 62, 6.3, 64, 65' from sesqui- oxide of chromium, 62, 63, 73 ; from sesquioxide of iron, 62, 70, 79, 91, 94. Sesquioxide of iron from alumina, 63, 64, 65, 69, 90 ; from sesquioxide of chromium, 63, 69, 73; from oxide of zinc, 62, 66, 77, 80, 89, 91 ; from protoxide of manganese, 62, 77, 78, 80, 92 ; from protoxide of nickel, 62, 67, 77, 78, 91 ; from protoxide of cobalt, 62, 67, 77, 81 ; from protoxide of iron, 62, 70, 79, 91, 94. A. General Methods. 1. Method based upon the Precipitation of some Oxides by Carbo- nate of Baryta. SESQUIOXIDE OF IRON, ALUMINA, AND SESQUIOXIDE OF CHROMIUM, FROM ALL OTHER OXIDES OF THE FOURTH GROUP. Mix the sufficiently dilute solution, which must contain a little 62 free acid,* in a flask, with a moderate excess of elutriated carbonate of * If there is much free acid, the greater part of it must first be saturated with carbo- nate of soda. SEPARATION OF THE BASES. 160.] baryta diffused in water ; insert the stopper and let the mixture stand some time in the cold, with occasional shaking. The sesquioxide of iron, alumina, and sesquioxide of chromium, are completely sepa- rated,* whilst the other bases remain in solution, with the exception perhaps of traces of protoxide of cobalt and protoxide of nickel, which will generally fall down with the precipitated oxides. This may be prevented, at least as regards nickel, by addition of chloride of am- monium to the fluid to be precipitated (Schwarzenberg, " Annal. d. Chern. u. Pharm.," 97, 216). Decant, stir the solid particles up with cold water, let deposit, decant again, filter, and wash with cold water. The precipitate contains, besides the precipitated oxides, carbonate of baryta ; and the nitrate, besides the non-precipitated oxides, a salt of baryta. If protoxide of iron is present, and it is wished to separate it by this method from sesquioxide of iron, &c., the air must be excluded during the whole of the operation. In that case, the solution of the substance, the precipitation, and the washing by decantation, are effected in a flask (see Fig. 78, A), through which carbonic acid is transmitted (d). The washing water, boiled free from air, and cooled out of con- tact of air, is poured in through a funnel tube (c), and the fluid drawn off by means of a moveable siphon (b) ; both b and c are fitted air- tight into the cork ; they are smeared with tallow. Fi S- 78. 337 2. Method based upon the Precipitation of the Oxides of the Fourth Group, by Sulphide of Sodium, from Alkaline Solu- tion effected with the aid of Tartaric A cid. ALUMINA AND SESQUIOXIDE OF CHROMIUM FROM THE OXIDES OF THE FOURTH GROUP. Mix the solution with tartaric acid, then with pure solution of 63 soda or potassa until the fluid has cleared again ;t add sulphide of sodium as long as a precipitate forms, allow it to deposit until the supernatant fluid no longer exhibits a greenish or brownish tint ; decant, stir the precipitate up with water containing sulphide of sodium, decant again, transfer the precipitate, which contains all the metals of the fourth group, to a filter, wash with water containing sulphide of sodium, and separate the metals as directed in B. Add to the filtrate nitrate of potassa, and evaporate to dryness ; fuse the residue, and separate the alumina from the chromic acid formed, as directed 157. * The separation of the sesquioxide of chromium requires the most time. T Sesquioxide of chromium and oxide of zinc cannot be obtained together in alkaline solution (Chuncel, "Compt. rend.," 43, 927; "Journ. L prakt. Chern.," 70, 378). II. Z 338 SEPARATION OP THE BASES. [ 160. B. Special Methods. 1. Methods based upon the Solubility of Alumina in Caustic Alkalies* a. ALUMINA FROM PROTOXIDE AND SESQUIOXIDE OF IRON, AND SMALL QUANTITIES OF PROTOXIDE OF MANGANESE (but not from the protoxides of nickel and cobalt). Heat the rather concentrated acid solution in a flask to boiling, 64 remove from the fire, and reduce the sesquioxide of iron present by sul- phite of soda. Replace the fluid on the fire, keep boiling some time, and then neutralize with carbonate of soda, add solution of pure soda or potassa in excess, and boil for some time. If the analysed substance contains much iron, the precipitate will become black and granular, which is a proof that the iron has been converted into protosesquioxide. The tendency to bumping, pre- ceding the actual ebullition of the fluid, may be guarded against by means of a spiral coil of platinum wire placed in the liquid, or by constant agitation of the latter ; when ebullition has once set in, there- is no further need of these precautions. Remove the fluid now from the fire, allow to deposit, pass the clear fluid through a filter, which must not be over-porous, boil the precipitate again with a fresh quantity of solution of soda, then wash it, first by de- cantation, afterwards on the filter with hot water. Acidify the alkaline filtrate with hydrochloric acid, boil with some chlorate of potassa (38)j concentrate by evaporation, and precipitate the alumina as directed 105, a (" Journ f. prakt. Chem.," 45, 261). The boil- ing of the precipitated oxides with the solution of soda is effected best in a somewhat capacious silver or platinum dish. A solution of soda containing alumina and silica must be particularly avoided. If sesquioxide of chromium was present in the analysed sub- stance, you will find the principal portion of this with the sesqui- oxide of iron ; but a small quantity has been oxidized in the process and converted into chromic acid, and is accordingly found in the fluid filtered from the alumina. b. The method described in a is often employed also in a modified form, omitting the reduction of the sesquioxide of iron ; in which case the process is performed as follows : Precipitate with ammonia, decant, filter, wash, transfer the precipitate still moist to a platinum dish, without the aid of water, and remove the last particles adhering to the filter by means of warm hydrochloric acid. The washings of the filter are kept separate. When the precipitate in the platinum dish has dissolved, add, very cautiously, concentrated solution of carbonate of soda, until the free acid is almost neutralized, then apply heat, finally to boiling; after this, remove the lamp, and add a lump of pure hydrate of potassa. sufficiently large to redissolve the precipitated alumina, leaving the hydrated sesquioxide of iron undissolved. Rinse the platinum dish now into the beaker which contains the washings of the filter ; wash the sesquioxide of iron, first by decantation, then upon the filter with boiling water, and treat the filtrate as in a. If the fluid from which it is intended to separate sesquioxide of iron : * Instead of solution of potassa or soda, ethylamine may also be used to effect the separation of alumina from iron (SonneTischcin, "Journ. f. prakt. Chem.," 67, 148). 1GO.] SEPARATION OP THE BASES. 339 and alumina, contains lime or magnesia, some alumina is likely to remain undissolved. c. ALUMINA FROM SESQUI- AND PROTOXIDE OF IRON, PROTOXIDE OF COBALT, AND PROTOXIDE OF NICKEL. Fuse the oxides with hydrate of potassa in a silver crucible, boil 65 the mass with water, and filter the alkaline fluid, which contains the alumina, from the oxides, which are free from alumina, but contain potassa (H. Rose). 2. Methods based upon the different deportment of the several Sul- phides with Acids, or of the Acetic Acid Solutions with Sul- phuretted Hydrogen. a. OXIDE OF ZINC FROM ALUMINA AND THE OXIDES OF THE FOURTH GROUP. The solution of the acetates, which must be free from inorganic 66 acids, and must contain a sufficient excess of acetic acid, is precipitated with sulphuretted hydrogen, which throws down the zinc only ( I 08, 6). The oxides are usually most readily obtained, in acetic acid solution, by converting them into sulphates, and adding a suffi- cient quantity of acetate of baryta. Sulphuretted hydrogen is then conducted, without application of heat, into the unfiltered fluid, to which, if necessary, some more acetic acid has been added. Should the precipitate, as will sometimes happen, look gray, this may be remedied, if the coloration proceeds from admixture of sulphide of iron in the precipitate, by applying a gentle heat, and once more con- ducting sulphuretted hydrogen into the fluid. The precipitate, which consists of a mixture of sulphide of zinc and sulphate of baryta, is washed with water containing sulphuretted hydrogen. It is then heated with hydrochloric acid, the solution filtered, and the zinc in the filtrate determined as directed 108, a. The other oxides in the fluid filtered off from the sulphide of zinc are, after previous removal of the baryta by precipitation, determined by the proper methods. b. PROTOXIDE OF COBALT AND PROTOXIDE OF NICKEL FROM PROTOXIDE OF MANGANESE AND THE OXIDES OF IRON. The solution of the oxides, which must be free from nitric acid, is, 67 after previous neutralization of any free acid which may be present by ammonia, precipitated with sulphide of ammonium, and highly dilute hydrochloric acid (H. Rose), or acetic acid ( Wackenroder) then added, and sulphuretted hydrogen gas conducted into the fluid to satu- ration, with frequent stirring. This serves to dissolve the sulphide of manganese and the sulphide of iron, whilst the sulphide of cobalt and the sulphide of nickel, though the latter less completely, remain undissolved. The sulphides of the metals are reprecipitated from the filtrate by addition of ammonia and sulphide of ammonium, and the precipitate is treated once more with dilute hydrochloric acid, &c. The results are nearly accurate. It is advisable, however, to test the weighed cobalt and nickel compounds, for manganese and iron. c. PROTOXIDE OF COBALT AND PROTOXIDE OF NICKEL FROM PROT- OXIDE OF MANGANESE AND OXIDE OF ZINC. a. Put the weighed mixture of the oxides in a small porcelain or 68 platinum boat, insert this into a tube, heat to dull redness, whilst conducting sulphuretted hydrogen gas over it. Let the sulphides of z 2 340 SEPARATION OF THE BASES. [ 160. the metals formed cool in the current of gas, and then digest them for several hours with cold dilute hydi-ochloric acid, which dissolves only the sulphide of manganese, and the sulphide of zinc. The sul- phides of nickel and cobalt are left behind free from admixture of the other sulphides {Ebelmen).* fi. Precipitate with carbonate of soda, filter, wash, and ignite; mix 1 part of the residue with 1/5 of sulphur and 0'75 of carbonate of soda, and heat the mixture in a small retort as strongly as possible for half an hour. Allow the mixture to cool, and treat the sulphide of zinc (and sulphide of manganese) formed, with dilute hydrochloric acid (1 part of acid to 10 of water), Brunner. 1 ^ 3. Methods based upon the different deportment of the several Oxides with Hydrogen Gas at a red heat. a. SESQUIOXIDE OF IRON FROM ALUMINA AND SESQUIOXIDE OF CHROMIUM. a. Rivots Method. (Ann. de Chim. et de Phys.," xxx 188 ; 69 "Journ. f. prakt. Chem.," 51, 338.) Precipitate with ammonia, heat, filter, ignite, weigh.. Triturate, and weigh off a portion of the powder, in a small porcelain boat. Insert the latter into a porcelain tube, lying in an horizontal position and having one end closed with a cork into which a narrower open glass tube is fitted. Conduct into the open end hydrogen gas, dried by transmission through sulphuric acid and chloride of calcium. When the air is expelled from the apparatus, heat the porcelain tube gradually to redness, and maintain it at that temperature as long as water forms (about 1 hour). Allow the tube now to cool in a current of hydrogen gas, then remove the little boat, and weigh it. The loss of weight indicates the quantity of oxygen which was combined with the iron to sesquioxkle. If you wish to determine the oxides separately, which may be deemed more particularly necessary if the analysed substance con- tains much alumina and little sesquioxide of iron, treat the mixture of alumina, sesquioxide of chromium, and metallic iron, with highly dilute nitric acid (1 part of acid to 30 or 40 parts of water), or with water to which very little nitric acid is gradually added. The iron is dissolved, the alumina and sesquioxide of chromium remain undis- solved. The latter oxides are weighed; the iron is precipitated from the filtrate by ammonia, after ebullition of the fluid. The results of Rivofs experimental analyses were highly satisfactory. The method is more particularly suitable in cases where the qxiantity of alumina is large, that of sesquioxide of iron small. /3. Demtte transmits through the tube, after the reduction by hydrogen has been effected as in a, first hydrochloric gas, and then again hydrogen. This leaves the alumina in a state of purity ; the iron volatilizes as protochloride, and is either determined in the direct way, or calculated from the loss. If it is intended to do the former, the protochloride in the tubes and in the tubulated receiver is dissolved by heating dilute hydrochloric acid to boiling, and conduct- ing the fumes into the porcelain tube ; the tubuluture of the receiver * " Annal. der Chem. und Pharm.," 72, 329. Ebelmen has given his method simply for the separation of CoO and NiO from MnO. t " Annal der Chem. und Pharm.," 80, 364. runncr has given his method simply for nickel and zinc. 160.] SEPARATION OP THE BASES. 341 is directed downwards in this operation. Deville has employed his method simply to effect the separation of sesqnioxide of iron from alumina; but it is obvious that it is equally adapted for the separa- tion of sesquioxide of iron from sesquioxide of chromium. SUPPLEMENT : Decomposition of Chrome-Iron (Rivot, " Journal f. prakt. Chem.," 51, 347). Treat the finely levigated mineral as directed in a. An hour's application of a bright red heat is sufficient to effect the complete re- duction of the protoxide of iron. The moss is allowed to cool in the stream of hydrogen gas, and then digested 24 hours with dilute nitric acid, which dissolves the iron, lime, and magnesia, leaving the sesqui- oxide of chromium, alumina, and silicic acid undissolved. b. SESQUIOXIDE OP IRON FROM PROTOXIDE OF IRON. Compounds containing only sesquioxide and protoxide of iron, or, 70 at all events, besides these two, no other substances liable to undergo alteration by ignition in a stream of hydrogen gas, are accurately weighed, intensely ignited in hydrogen gas, allowed to cool in the gaseous current, and then again weighed ; the loss of weight indicates the quantity of oxygen originally combined with the iron. The quantity of iron may be determined, according to circumstances, either by simply weighing the residue, or by an ulterior analysis of the latter. The operation may be conducted either as in a, or in a bulb-tube. If, by way of control, you wish to weigh the water gene- rated in the process of reduction, you may use the apparatus described 1 in 36, and illustrated by Fig. 37. The gasometer is, in that case, to be filled with hydrogen gas instead of atmospheric- air. c. PROTOXIDE OF COBALT AND PROTOXIDE OF NICKEL FROM OXIDE OF ZINC. Ullgreris Method. (Berzelius 1 s " Jahresbericht," 21, 145.) Precipitate the solution with carbonate of soda, in the manner and 71 with the precautions directed in 108, a. Wash the precipitates carefully with boiling water, dry, ignite, and weigh. Triturate finely, introduce a weighed portion of the powder into the bulb of a bulb-tube, aiid heat the latter to incipient redness, transmitting a slow current of hydrogen gas through it during the operation. As soon as the formation of water ceases, stop the application of heat, and allow the mass to cool in the hydrogen stream. The mass con- tains the whole of the cobalt and nickel in the metallic state, the whole of the zinc as oxide. Close one end of the tube by fusion, fill up with a concentrated solution of carbonate of ammonia, insert a cork into the other end, keeping the tube for 24 hours at a gentle heat (about 1 04 F.). The oxide of zinc dissolves completely; the undissolved portion, which consists of the cobalt and nickel, is washed repeatedly with solution of carbonate of ammonia, then dried and weighed. The quantity of the oxide of zinc is found by cautiously evaporating the ammoniacai solution, and igniting the residue. The cobalt invariably retains some aTkali. 4. Method based upon tJie different deportment of the Chlorides of the Metals with Hydrogen at a Red Heat. PROTOXIDE OF COBALT AND PROTOXIDE QF NICKEL FROM PROT- OXIDE OF MANGANESE. 342 SEPARATION OF THE BASES. [ 160. The oxides are thrown down from the solution; if the latter is free 72 from salts of ammonia, this is effected by precipitating with solution of soda; but in presence of a considerable proportion of salts of am- monia, the best way is to precipitate with sulphide of ammonium, wash the sulphides of the metals thrown down, dissolve in nitro- hydrochlorie acid, and precipitate with solution of soda. The precipitated oxides, or a weighed portion of them, are intro- duced into a bulb-tube, and exposed, in a current of dry hydrochloric gas, to a moderate red heat, until they are completely converted into chlorides, and consequently until the formation of water has entirely ceased, which takes a long time to accomplish. A strong heat is now applied to the bulb, and dry hydrogen gas transmitted over the chlorides until a slight cloud only is perceptible upon approaching a glass rod moistened with ammonia to the mouth of the tube. The protochlorides of nickel aud cobalt are reduced to the metallic state in this process, whilst the protochloride of manganese remains un- altered. The mass is allowed to cool in the current of hydrogen gas, and the bulb-tube is then placed in a cylinder with water. The greater part of the protochloride of manganese dissolves, a small portion floating about in the fluid in the form of brown flakes ; the cobalt and nickel speedily subside. The fluid, with the suspended light flakes in it, is decanted from the reduced metals, and the latter washed on a weighed filter first with a little highly dilute hydro- chloric acid, then with water dried, and weighed (compare also 111, 6). The decanted fluid, with the washings together with some hydrochloric acid, is concentrated by evaporation, and the man- ganese precipitated with carbonate of soda ( 109). The results are accurate (H. Rose). 5. Methods based upon the different capacity of the several Oxides to be converted by Oxidizing Agents into higher Oxides, or by Chlorine into higher Chloi'ides. a. SESQUIOXIDE OF CHROMIUM FROM ALL THE OXIDES OF THE FOURTH GROUP. Fuse the oxides with nitrate of potassa and carbonate of 7J soda (compare 157), boil the mass with water, add a sufficient quantity of spirit of wine, and heat gently for several hours. Filter, and determine in the filtrate the chromium as directed 130, and in the residue the bases of the fourth group. The following is the theory of this process : the oxides of zinc, cobalt, nickel, iron, and partly that of manganese, separate upon fusion with nitrate of potassa and carbonate of soda, whilst, on the other hand, manganate (perhaps also some ferrate) and chromate of potassa are formed. Upon boil- ing with water, part of the manganic acid of the manganate of potassa is converted into permanganic acid at the expense of the oxygen of the other part, which is reduced to the state of binoxide ; the latter separates, whilst the potassa salts are dissolved. The addition of alcohol, with the application of a gentle heat, effects the decom- position of the permanganate of potassa, and the reduction of the permanganic acid to the state of binoxide of manganese, which separates. Upon filtering the mixture, we have therefore now the whole of the chromium in the filtrate as alkaline chromate, and all the oxides of the fourth group on the filter. ' 160.] SEPARATION OP THE BASES. 343 The analysis of the native compound of sesquioxide of chromium with protoxide of iron (chrome-iron), requires the most careful elu- triation of the mineral, and long-protracted fusion with the proper flux. However, in most cases, even the strictest attention to these points will not prevent part of the mineral remaining undecomposed ; in which case the residue left undissolved by water will not completely dissolve in hydrochloric acid. In cases of this kind, the best way is to proceed as follows : Fuse 8 parts of borax in a platinum cru- cible, add to the mass in fusion 1 part of the finely pulverized ore, and keep the crucible half an hour longer at a bright red heat ; add dry carbonate of soda as long as it causes effervescence, then gradu- ally, and with frequent stirring with a platinum wire, 3 parts of a mixture of equal parts of nitrate of potassa and carbonate of soda, and keep the mass a few minutes longer in fusion. The sesquioxide of chromium is by this process completely converted into chromated alkali, which is then dissolved out by boiling with water. The resi- due must completely dissolve in hydrochloric acid (Hart, "Chem. Gaz.," 1855, 458). Calvert ("Chem. Gaz.," 1852, p. 280) recommends to effect the decomposition of the chrome-ores, by mixing the finely pulverized minerals with 3 4 parts of soda-lime and 1 part of nitrate of soda, and fusing the mixture for two hours. b. PROTOXIDE OF MANGANESE FROM ALUMINA, PROTOXIDE OF NICKEL, AND OXIDE OF ZINC (but not from protoxide of cobalt and the oxides of iron). Gibbss Method (" Annal. d. Chem. u. Pharm.," 66, 56). Precipi- 74 tate the manganese with binoxide of lead, and proceed exactly as for the separation of manganese from magnesia. c. PROTOXIDE OF MANGANESE FROM ALUMINA, PROTOXIDE OF NICKEL, AND OXIDE OF ZINC (but not from protoxide of cobalt and the oxides of iron). SchieVs Method.* Conduct chlorine gas into the solution mixed 75 with acetate of soda (see 58, ft). . Compare also Rivot, Beudant and Daguin, "Coinpt. rend.," 1853, 835 ; " Journ. f. prakt. Chem.," 61, 130. d. PROTOXIDE OF COBALT AND PROTOXIDE OF MANGANESE FROM PROTOXIDE OF NICKEL (H. Rose, "Pogg. Annal.," 71, 545). Dilute the hydrochloric acid solution, in a capacious flask, with 76 1 litre of water to 2 grms. of metallic oxides in the solution, conduct chlorine gas into the flask until the fluid is saturated, and the vacant space in the flask completely filled with the gas ; add elutriated carbonate of lime in excess, let the mixture stand in the cold from 12 to 18 hours, taking care to shake repeatedly ; then, filter the fluid, which contains the whole of the nickel, from the pre- cipitated sesquioxide of cobalt and manganese. Henry has employed bromine instead of chlorine as the oxidizing agent ; he obtained satisfactory results. Denham Smith recommends addition of a dilute solution of chloride of lime which has been com- pletely decomposed by addition of sulphuric acid, so as to leave no * " Sillim. Journ.," 15, 275. Sckiel speaks only of the separation of the manganese from iron and nickel ; but it is obvious that its separation from alumina and zinc may be effected by the same method. 344 SEPARATION OF THE BASES. [ 160. particle of tmdecomposed hypochlorite (otherwise nickel would be thrown down with the other oxides). 6. Method based upon the different deportment of tJte Succinates of the several Oxides. SESQUIOXIDE OF IRON FROM OXIDE OF ZINC, PROTOXIDE OF MAN- GANESE, PROTOXIDE OF NICKEL, AND PROTOXIDE OF COBALT. Add to the solution, if not strongly acid, chloride of ammonium, 77 then neutralize with ammonia so as to precipitate a very small portion of the sesquioxide of iron, leaving the greater part in solu- tion; add now a solution of neutral succinate (or benzoate) of ammo- nia, and filter the fluid from the succinate of sesquioxide of iron ; the filtrate contains the other metallic oxides. For the details of the process, see 113, 1 c. With proper care, the separation is com- plete ; the process is more particularly adapted for cases where the relative proportion of the sesquioxide of iron is rather large. 7. Methods based upon the deportment of neutralized Solutions of the Oxides at boiling heat. a. SESQUIOXIDE OF IRON FROM THE PROTOXIDES OF MANGANESE AND NICKEL AND OTHER STRONG BASES. Mix the dilute solution largely with chloride of ammonium (at 78 least 20 N H 4 Cl to 1 of oxide), add highly dilute solution of car- bonate of ammonia in small quantities, at last drop by drop, as long as the precipitated iron redissolves, which takes place promptly at first, but more slowly towards the end. As soon as the fluid has lost its transparency, without showing, however, the least trace of a distinct precipitate in it, and fails to recover its clearness after standing some time in the cold, but, on the contrary, becomes rather more turbid than otherwise, the reaction may be considered completed. When this point has been attained, heat slowly to boiling, and keep in ebul- lition for a short time after the carbonic acid has been entirely expelled. The sesquioxide of iron separates as a basic salt, promptly if the solution was not too highly concentrated. Add now a drop of ammonia, to see whether the irdh has been completely thrown down, then some more ammonia, to convert the basic salt of iron, which has a tendency to dissolve upon cooling, into hydrated sesqui- oxide, and filter. To ensure accurate results, the fluid must not contain more than 3 '4 grms. of sesquioxide of iron in the litre, and must be tolerably free from sulphuric acid, since it is difficult in presence of the latter to hit the exact point of saturation. Herschel (" Anual. de Chem. et de Phys.," 49, 306) ; Schwarzenberg (" Annal. d. Chem. u. Pharm.," 97, 216). b. SESQUIOXIDE OF IRON FROM THE PROTOXIDE. In compounds which dissolve with difficulty in hydrochloric acid, 79 but are decomposed by moderately concentrated sulphuric acid at a temperature below 618-8 F* Scheerer ("Pogg. Annal.," 86, 91, and 03, 448) separates sesquioxide from protoxide of iron, by effecting the solution in an atmosphere of carbonic acid, kept up during the experiment, diluting with pieces of ice free from air, adding carbonate of ammonia until the acid is nearly neutralized, then finely powdered magnesite (but not magnesia alba), and boiling * Upon boiling, protoxide of iron is peroxidized, the sulphuric acid being reduced to sulphurous acid. Kobdl (" Annal. der Chem. u. Phariu.," 90, 244). 160.] SEPARATION OF THE BASES. 345 from 10 to 18 minutes. The whole of the sesquioxide of iron is precipitated by this process. The precipitate is washed as in 62, with water which, after being mixed with some sulphate of ammonia, has been boiled free from air and allowed to cool out of contact of air. Kobell (" Annal. d. Chem. u Pharm.," 90, 244) prefers, as dis- solving agent, a mixture of 1 vol. of concentrated sulphuric acid, 2 vols. of water, and 1 vol. of strong hydrochloric acid. 8. Met/tod based upon the deportment of the Acetates of the Oxides at boiling heat. ALUMINA AND SESQUIOXIDE OP IRON FKOM PROTOXIDE OF MAN- GANESE AND OXIDE OF ZINC. See 57, d, and 113, 1, d. Results satisfactory. 80 9. Method based upon the different deportment of the Oxalates of the several Oxides. PROTOXIDE OF COBALT FROM SESQUIOXIDE OF IRON. Mix the solution, which must be as neutral as possible, with bin- 81 oxalate of potassa (or with oxalic acid and a sufficient quantity of carbonate of potassa to leave the reaction only moderately acid), and allow the mixture to stand at rest for 3 or 4 days, shaded from sun- light. The oxalate of protoxide of cobalt separates completely, free from iron. Wash with cold water, ignite in a stream of hydrogen gas, and weigh the metallic cobalt. The results are satisfactory (H. Rose). 10. Method based upon the different deportment of the Nitrites of the several Oxides. PROTOXIDE OF COBALT FROM PROTOXIDE OF NICKEL, ALSO FROM PROTOXIDE OF MANGANESE AND OXIDE OF ZINC. The cobalt is precipitated as nitrite of sesquioxide of cobalt and 82 potassa, as directed 111, 4. The other bases remain in solution (Fischer, " Pogg. Annal.," 72, 477 ; A. Stromeyer, " Annal. d. Chem. u. Pharm.," 96, 218). 11. Methods based upon tfo different deportment of the several Oxides with Cyanide of Potassium. a. ALUMINA FROM OXIDE OF ZINC, PROTOXIDE OF COBALT, AND PROTOXIDE OF NICKEL. Mix the solution with carbonate of soda, add cyanide of potassium 83 iu sufficient quantity, and digest in the cold, 'until the precipitated carbonates of oxide of zinc and protoxide of cobalt and protoxide of nickel are redissolved. Filter the fluid from the undissolved alumina, wash the latter, and remove the alkali which it contains, by redis- solving in hydrochloric acid and reprecipitation by ammonia (Frese- nius and Haidlen, "Anna!, d. Chem. u. Pharm.," 43, 12U). b. PROTOXIDE OF COBALT FROM PROTOXIDE OF NICKEL. Liebigs Method (" Annal. d. Chem. und Pharm.," 65, 244). -Mix 84 the solution of the two oxides, which must be free from other oxides, with hydrocyanic acid, then with solution of potassa, and warm, until the precipitate first formed is completely redissolved. (Cyanide of potassium, free from cyanate, may be used instead of hydrocyanic acid and potassa.) The solution looks reddish-yellow ; heat to boiling to remove the free hydrocyanic acid. By this process the double cyanide 346 SEPARATION OF THE BASES. [ 160. of cobalt and potassium (K Cy, Co Cy) in the solution is converted, with evolution of hydrogen, into cobalticyanide of potassium,* whilst the double cyanide of nickel and potassium in the solution remains un- altered. Add to the hot solution finely pulverized and elutriated oxide of mercury, and boil. By this operation the whole of the nickel is pre- cipitated partly as sesquioxide partly as protocyanide, the mercury combining with the liberated cyanogen. If the fluid was neutral before the addition of the oxide of mercury, it shows alkaline re- action after boiling with the latter. The precipitate looks greenish at first, or, if the oxide of mercury has been added in excess, yellow- ish-gray. Wash and ignite. The residue is pure protoxide of nickel. To determine the cobalt in the filtrate, supersaturate with acetic acid, boil, precipitate the boiling solution with sulphate of copper, keep in ebullition for some time longer, then filter the fluid from the precipi- tated cobalticyanide of copper (Cu 3 , Co 2 Cy s , + 7 H O) ; decompose the latter by boiling with solution of potassa, and calculate the quantity of the cobalt from that of the oxide of copper obtained. The follow- ing method, recommended by WoJiler (" Annal. d. Chem. und Pharm.," 70, 256), is more simple and convenient. The filtrate is nearly neutralized with nitric acid (a slight alkaline reaction is of no consequence), and a perfectly neutral solution of nitrate of sub- oxide of mercury added ; the white precipitate of cobalticyanide of mercury, which contains the whole of the cobalt, may be readily washed, and gives, upon ignition, with free access of air, pure proto- sesquioxide of cobalt ; the reduction of the latter is effected best with hydrogen. See 111. Instead of precipitating the nickel with oxide of mercury, proceed as follows : after expelling the free hydrocyanic acid by boiling, let the solution cool, then supersaturate with chlorine, and redissolve the precipitate of cyanide of nickel which forms, by addi- tion of solution of soda or potassa. The chlorine does not act upon the cobalticyanide of potassium, but it decomposes the double cyanide of nickel and potassium, and throws down the whole of the nickel as black peroxide (Liebig, "Annal. d. Chem. u. Pharm.," 87, 128). c. PROTOXIDE OP COBALT FROM OXIDE OF ZINC. Add to the solution of the two oxides, which must contain some 85 free hydrochloric acid, common cyanide of potassium (prepared after Liebig 's method), in sufficient quantity to redissolve the precipitate of protocyanide of cobalt and cyanide of zinc which forms at first ; then add a little more cyanide of potassium, and boil some time, adding occasionally one or two drops of hydrochloric acid, but not in sufficient quantity to make the solution acid. Mix the solution with hydrochloric acid in an obliquely placed flask, and boil until the cobalticyanide of zinc which precipitates at first is redissolved, and the hydrocyanic acid completely expelled. Add solution of soda or potassa in excess, and boil until the fluid is clear ; the solution may now be assumed to contain all the cobalt as cobalticyanide of potas- sium, and all the zinc as a mixture or compound of oxide of zinc and alkali. Precipitate the zinc by sulphuretted hydrogen ( 108). Filter, and determine the cobalt in the filtrate as in 84- The process is simple and the separation complete (Fresenius and Haidlen). * 2 (Co Cy, K Cy) + K Cy + H Cy = (K,, Co, Cy 6 ) + H. 160.] SEPARATION OF THE BASES. 347 d. PKOTOXIDE OF COBALT PROM PROTOXIDE OP MANGANESE. Mix the solution of the two oxides with hydrocyanic acid, then 86 with solution of potassa and soda, and warm the mixture. If the quantity of hydrocyanic acid added was sufficient, the precipitated protocyanide of cobalt redissolves completely, whilst the greater por- tion of the precipitated protocyanide of manganese remains undissolved. Filter, and treat the filtrate exactly as in 84 (Separation of Cobalt from Nickel). Ignite the two manganese precipitates together. When the oxide of mercury which the second manganese precipitate contains in admixture, has been expelled, there remains protosesquioxide of manganese. This shows that cobalt may be separated also both from nickel and manganese at the same time ; in which case the dissolved portion of the manganese is obtained with the protoxide of nickel (Comp. also Flajolot, " Journ. prakt. Chem.," 61, 110). e. PROTOXIDE OF NICKFL FROM OXIDE OF ZINC. Mix the concentrated solution of both oxides with an excess of 87 concentrated pure solution of potassa, then with solution of hydro- cyanic acid in sufficient quantity to redissolve the precipitate com- pletely ; add solution of sulphide of potassium (K S), allow the pre- cipitated sulphide of zinc to deposit at a gentle heat, filter, and determine the nickel in the filtrate by heating for some time with fuming hydrochloric acid and nitric acid, or, instead of the latter, with chlorate of potassa, evaporating, and finally precipitating with potassa (Wohler, " Annal. d. Chem. u. Pharm.," 89, 376). 1 2. Methods based upon the Volatility of Zinc. a. PROTOXIDE OP COBALT AND PROTOXIDE OF NICKEL FROM OXIDE OP ZINC. Berzelius (" Jahresbericht, " 21, 144) recommends the following 88 method for the absolute separation of cobalt and nickel from zinc. Precipitate with solution of potassa in excess, boil, and filter the fluid, which contains the greater portion of the zinc dissolved in the caustic potassa, from the precipitated hydrate of protoxide of nickel and cobalt, which also contains some of the zinc ; wash the precipi- tate thoroughly with boiling water, and determine the zinc in the filtrate as directed 108. Dry the precipitate, ignite, and weigh ; then mix in a poi-celain crucible with pure sugar (r eery stall ized from solution in alcohol), and heat slowly until the sugar is com- pletely carbonized. Place the crucible, with the lid on, in a bath of magnesia in a larger-sized covered clay crucible, and expose for the space of 1 hour to the very highest degree of heat attainable by a wind furnace. This process causes the reduction of the metals : the whole of the zinc present rises in vapor, the nickel and cobalt, mixed with charcoal, remain. Treat the residue with nitric acid, and determine the oxides by precipitating with solution of potassa, and weighing the precipitate. The difference between this weight and that ob- tained before, shows the quantity of the oxide of zinc which has been thrown down with the other oxides. This method gives very accurate results only in the separation of nickel from zinc (Compare 111, b). b. ZINC FROM IRON, IN ALLOYS. Bobierre states that these alloys may be readily and accurately 89 analysed by igniting them in a stream of hydrogen gas (see 115). 348 SEPAKATION OF THE BASES. [ 160. 13. Methods based upon the Volumetric Determination of one of the Oxides, and the calculation of the other from the difference. a. SESQUIOXIDE OF IRON FROM ALUMINA. Precipitate both oxides with ammonia ( 105, a, and 113, '!). 90 Dissolve the weighed residue, or an aliquot part of it, by digestion with concentrated hydrochloric acid, or by fusion with bisulphate of potassa and treating with water containing hydrochloric acid ; and determine the iron volumetrically as directed 113, 2. Calculate the alumina from the difference. This method is to be recommended more particularly in cases where the relative proportion of the ses- quioxide of iron is small. In the analysis of larger quantities, it is of course much more convenient to divide the solution, by weighing or measuring, into 2 equal portions, and determine in the one the sesquioxide of iron + alumina, in the other the iron. Instead of estimating the iron by volumetric analysis, you may also precipitate it, after addition of tartai-ic acid and ammonia, with sulphide of ammonium. b. SESQUIOXIDE OF IRON FROM PROTOXIDE OF IRON (OXIDE OF ZINC, PROTOXIDE OF NICKEL). a. Determine in a portion of the substance the total amount of 91 the iron as sesquioxide, or by the volumetrical way. Dissolve another portion by warming with hydrochloric acid in a flask through which carbonic acid is conducted, to exchide the air ; dilute the solution, and determine the protoxide of iron volumetrically ( 112, 2, a). The difference gives the quantity of the sesquioxide. This convenient and accurate method will probably replace the more complicated methods hitherto employed, to determine protoxide of iron in pre- sence of sesquioxide. If the compound in which sesqui- and prot- oxide of iron are to be estimated, is only with difficulty decomposed by acids, fuse 1 part of it with 5 or 6 parts of fused borax, in a small retort, connected with a flask containing nitrogen (produced by com- bustion of phosphorus in the air) ; an atmosphere of carbonic acid is less suitable. Triturate the fused mass, and dissolve the powder in, boiling hydrochloric acid, in an atmosphere of carbonic acid (Her- mann ; v. Kobell], Iron may also be determined volumetrically in presence of oxide of zinc, protoxide of nickel, &c. It is, indeed, often the better way, instead of effecting the actual separation of the oxides, to determine in one portion of the solution the sesquioxide of iron + oxide of zinc or + protoxide of nickel, in another portion the iron alone, and to find the quantity of sesquioxide by the difference. However, this can be done only in cases where the quantity of iron is relatively small. ft. Bunseris method. Fill the little flask d (Fig. 65, 130) two- thirds with fuming hydrochloric acid, and expel the air above by car- bonic acid, by throwing some fragments of carbonate of soda into the flask . Weigh a portion of the substance in an open short tube, and in another similar tube a slight excess of bichromate of potassa ; drop the two tubes into the flask, attach the evolution tube, and pro- ceed for the rest as directed 130, d, ft. Of course you will obtain less free iodine than if no protoxide of iron had been dissolved with the chromate of potassa, as a portion of the liberated chlorine 160.] SEPARATION OF THE BASES. 349 goes to convert the protochloride of iron into sesquichloride ; each equivalent of iodine obtained less than corresponds to the chromate of potassa used, is calculated as 2 equivalents of protoxide of iron. If you wish to ascertain the total quantity of iron contained in the analysed substance, dissolve another portion of it in hydrochloric acid in the flask a (Fig. 79), and effect the reduction of the sesquioxide of iron to protoxide, by means of a ball of chemically pure zinc, cast on a fine platinum wire. To exclude all access of air, connect the flask, during the ebullition, with the apparatus b b' (Fig. 79). As soon as the colorless condition of the fluid shows that the reduction is completed, cool the flask in cold water, lift the upper cork, throw a few grains of carbonate of soda into the acid, draw the zinc ball up the tube b, wash off the fluid adhering to the ball into the flask, and remove b b'. Fi g . 79, Add quickly a weighed slight excess of bichromate of potassa, attach the evolution tube, and proceed for the rest as just directed. c. PROTOXIDE OF MANGANESE FROM ALUMINA AND SESQUIOXIDE OF IRON (Krieyer, " Annal. d. Chem. u. Pharm.," 87, 261). Precipitate with carbonate of soda, digest the precipitate some 92 time with the fluid, wash properly, first by decantation, then on the filter, dry, ignite, and determine in a sample the manganese as in 59 Bear in mind that the precipitate contains the manganese as Mn 3 O 4 . d. PROTOXIDE OF MANGANESE FROM OXIDE OF ZINC (Krieger). Precipitate boiling with carbonate of soda, wash the precipitate 93 with boiling water, dry, and ignite. If the analysed substance con- tained a sufficient quantity of zinc, the precipitate consists of Zn O + x Mn 2 O 3 . Weigh off a portion and determine in this the manga- nese as in 59- N.B. If the quantity of zinc is insufficient, proceed as directed 59- 14. Indirect Method. SESQUIOXIDE OF IRON FROM PROTOXIDE. Of the many indirect methods proposed, which are now, however, 94 but rarely resorted to since the employment of solution of perman- ganate of potassa for the volumetric determination of iron, I will only give the following : Dissolve as in 91> a dd solution of sodio- terchloride of gold in excess, close the flask, and allow the reduced gold to deposit ; filter the fluid from the gold, and determine the latter as directed 123. Determine the total quantity of the iron in the filtrate, or in another portion of the substance. The calcula- tion is self-evident : 1 equivalent of gold separated corresponds to 6 ' 350 SEPARATION OV THE BASES. [ 161. equivalents of protochloride or protoxide of iron (6 Fe Cl + Au Cl = 3Fe s Cl,-J-Au). (H.Rose.) IV. SEPARATION OF SESQUIOXIDE OP IRON, ALUMINA, PROTOXIDE OP MANGANESE, LIME, MAGNESIA, POTASSA, AND SODA. 161. As these oxides are found together in the analysis of most silicates, and also in manj other cases, I devote a distinct paragraph to the description of the methods which are employed to effect their sepa- ration. 1. Method based upon the employment of Carbonate of Baryta as Precipitant (particularly applicable in cases where the mix- ture contains only a small proportion of lime). Precipitate the iron which must be present in the form of ses- 95 quioxide and the alumina by carbonate of baryta,* and separate the two metals, after removing the baryta, by one of the methods given in 160. Precipitate the manganese from the filtrate, either by yellow sulphide of ammonium, or, after addition of a little hydro- chloric acid and saturation with chlorine, by carbonate of baryta, or, as Gibbs recommends, by binoxide of lead. If you have used sulphide of ammonium, dissolve the precipitated sulphide of manganese in hydro- chloric acid, mix the solution with some sulphuric acid, filter, and determine the manganese as directed 109, 1, a. If you have used carbonate of baryta as precipitant, separate the manganese as directed 159 ; if binoxide of lead, proceed as directed 162. Precipitate the dilute solution now with dilute sulphuric acid, filter, and wash the precipitate until the water running off is no longer rendered tui'bid by chloride of barium ; throw down the lime from the fil- trate with oxalate of ammonia, after having previously removed, by means of sulphuretted hydrogen, the last traces of lead, if the bin- oxide of that metal has been used as precipitant. Filter, evaporate the filtrate to dryness, ignite the residue, and separate the magnesia from the alkalies by one of the methods given in 153. In cases where the proportion of the alumina is large, that of the iron and manganese small, the solution may be saturated first with chlorine, and the sesquioxide of iron, alumina, and sesquioxide of manganese may then be jointly pi'ecipitated by carbonate of baryta, the precipitate dissolved in hydrochloric acid, the baryta thrown down from the solution by the least excess of sulphuric acid, then the three bases by carbonate of soda, and the precipitate tho- rougldy washed, dried, ignited, and weighed ; it contains the manga- nese as Mn s O 4 . If this and the sesquioxide of iron are now deter- mined by the volumetrical method, the difference will give the quantity of the alumina. It will be readily seen that one and the same sample may be used, first, for the determination of the manga- nese, and then for that of the iron ; compare 92 an d 90- There is only one objection to this method, namely, that it is apt to give a trifling excess of alumina, as that substance, when precipitated by a * Before adding the carbonate of baryta, it is absolutely indispensable to ascertain whether a solution of it in hydrochloric acid is completely precipitated by sulphuric acid, so that the filtrate leaves no residue upon evaporation on platinum. 161.] SEPARATION OF THE BASES. 35 1 fixed alkali, can hardly ever be altogether freed from the latter by washing. The joint precipitation of the alumina, iron, and manga- nese, may also be effected by ammonia, after previous saturation of the fluid with chlorine, or addition of hypochlorous acid. But, in that case, it is advisable to let the precipitated fluid stand at rest some time in a closed flask, and then to filter with exclusion of air. Care must also be taken to ascertain that the filtrate contains no manganese, which may be known by adding sulphide of ammonium, and allowing it to stand some time. 2. Method based upon the application of Acetates of the Alkalies as Precipitants. Remove from the solution, by evaporation, any very considerable 96 excess of acid which might be present, then dilute again with water, add carbonate of soda,* until the fluid is nearly neutral, t then ace- tate of soda, and proceed as in 57, d. Wash the precipitate well, dry, ignite, and weigh. Dissolve in concentrated hydrochloric acid,J and determine the iron by the volumetrical method given in 113, 2 ; the difference gives the quantity of the alumina. The filtrate contains the manganese, the alkaline earths, and the alkalies. Pre- cipitate the manganese with chlorine (58. /3), then the lime with oxalate of ammonia, and the magnesia, lastly, with phosphate of soda. However, if it is intended to estimate the alkalies, the mag- nesia must be separated as in 18- This method is convenient, and gives good results. It is often employed in my laboratory. 3. Metlwd based upon the application of Sulphide of Ammo- nium as Precipitant. Mix with ammonia until a precipitate just begins to form, then add 97 yellowish sulphide of ammonium, allow the precipitate which con- tains iron, manganese, and alumina to subside, and then filter. Separate the lime, magnesia, and alkalies in the filtrate as in 96- Dissolve the precipitate in hydrochloric acid, and separate the alu- mina from the iron and manganese by caustic potassa (64), and then the iron from the manganese by succinate of ammonia. The following methods are particularly suitable in cases where no manganese is present, or only inappreciable traces : 4. Metlwds based upon the application of Ammonia as Precipi- tant. a. Precipitate the alumina and sesquioxide of iron with ammonia 98 (see 38)- The precipitate is apt to contain a small admixture of lime, and a somewhat more considerable one of magnesia, whilst, on the other hand, some alumina often remains in solution. Wash by repeated decantation, finally on the filter. Separate the alumina in the precipitate by hydrate of potassa (64)- Dry the precipitate, which consists principally of hydrated sesquioxide of iron, and ignite ; dissolve the residue by digestion with fuming hydrochloric acid, filter, * In cases where it is intended to estimate the alkalies in the filtrate, carbonate and acetate of ammonia must be used instead of the soda salts. t The addition of the carbonate of soda (or ammonia) must not be continued until a permanent precipitate begins to form. t A small portion of the precipitate will often remain undissolved ; this consists of silicic acid, which must be filtered off, washed, dried, ignited, and weighed. 352 SEPARATION OF THE BASES. [ 161. if necessary, from the residuary silicic acid, and then precipitate the sesquioxide of iron by ammonia. Filter, and add the filtrate, which contains a little lime and magnesia, to the first fluid, which contains the bulk of these bases ; concentrate strongly, best in a platinum dish, precipitate, by ammonia, the trace of alumina which still re- mains in solution, and then separate the lime from the magnesia in the filtrate. If it is also intended to estimate the alkalies, the traces of lime and magnesia which have been thrown down with the sesquioxide of iron must be determined separately, as the solution of these two earths generally retains some of the alkali added to effect the separation of the alumina. Manganese, if present, is obtained partly in the precipitate partly in the solution, which tends to inter- fere with the process. However, by saturating the fluid with chlo- rine before precipitating by ammonia, the whole of the manganese, at least if present in small proportion only, is obtained in the precipi-. tate. b. Precipitate the alumina, sesquioxide of iron, and lime, by addi- 99 tion of ammonia and carbonate and oxalate of ammonia, decant, and filter. Dissolve the precipitate in hydrochloric acid, add tartaric acid, to prevent the precipitation of sesquioxide of iron and alumina, and then precipitate the lime with ammonia as oxalate. Filter, and separate the iron fix>ni the alumina in the filtrate as in 63 j aQ d the magnesia and alkalies in the first filtrate as in 18- Should the first filtrate contain sulphuric acid, remove this by chloride of barium, then separate the alkaline earths from the alkalies by eva- poration with oxalic acid, ignition, and treating the residue with boiling water, and finally the baryta from the magnesia as in 19- Mitscherlich; Lewinstein. " Journ. f. prakt. Chem.," 68, 99. c. Wash the ammonia precipitate carefully, dry, and ignite; add, 1QO without reducing the residue to powder, at least 10 times the quan- tity of anhydrous carbonate of soda, cover the crucible, and heat the mixture over the blast gas-lamp or some other appropriate sotirce of heat (the heat of a spirit-lamp with double draught is not sufficiently powerful), until decomposition of the carbonate of soda is no longer observable, at least 45 minutes. Boil the fused mass, best in a silver dish, after addition of some caustic potassa, with water until thoroughly extracted ; add, if manganate of soda imparts a green tint to the solution, a few drops of alcohol, and wash the precipitate by decantation and filtration, first with water con- taining potassa, then with pure water. Dissolve the washed precipitate in hydrochloric acid, heat, with addition of a few drops of alcohol, to facilitate the reduction of the sesquichloride of man- ganese, and separate finally, by means of acetate of ammonia, the sesquioxide of iron from the manganese, lime, and magnesia con- tained in the ammonia precipitate, which may then be either separately estimated, or determined jointly with the principal bulk of these alkaline earths. The alumina is determined in the alkaline solution as in 64 (& Richter, "Journ. f. prakt. Chem.," 64, 378). 5. Met/tod based upon the Decomposition of the Nitrates (Devilled method). This method presupposes that the bases are combined with nitric 101 acid only. 161.] SEPARATION OF THE BASES. 353 Proceed first as in 39- The escape of nitrous acid fumes observed during the heating of the nitrates, is no proof of the total decomposition of the nitrates of sesquioxide of iron and alumina, as these vapors may owe their formation to the conversion of the nitrate of protoxide of manganese into binoxide. Stop the appli- cation of heat when no more vapors are evolved, and the substance has acquired a uniform black color. After the treatment with nitrate of ammonia, the solution contains nitrate of lime, nitrate of magnesia, and nitrates of the alkalies, the residue contains alumina, sesqui- oxide of iron, and binoxide of manganese. That some manganese is dissolved, under certain circumstances, has been stated already in 58> yj the small quantity of manganese which has thus got into the solution, is found with the magnesia, and finally separated from the latter. Deville recommends the following methods to effect the further separation of the bases. a. Heat the residue with moderately strong nitric acid, until the alumina and sesquioxide of iron are dissolved, leaving the residuary binoxide of manganese of a pure black color. Ignite the residue, and weigh the protosesquioxide of manganese formed. Evaporate the solution in a platinum crucible, ignite, and weigh the mixture of sesquioxide of iron and alumina, which may possibly also contain some protosesquioxide of manganese. Treat a portion of it by the method described in 69 ; this gives the weight of the alumina. If manganese was present, the iron cannot be estimated by the difference. Deville therefore evaporates the solution of the proto- chlorides (69> /3) with sulphuric acid, ignites gently, and treats the residue, which consists of sesquioxide of iron and some sulphate of protoxide of manganese, with water to dissolve the latter. Should the heat applied have been too strong, which might possibly lead to the decomposition also of sulphate of protoxide of manganese, the residue is moistened with a mixture of oxalic acid and nitric acid, some sulphuric acid added, and the process repeated. b. From the filtrate, precipitate first the lime by oxalate of ammonia, then separate the magnesia from the alkalies as directed 153, 4. This method is particularly suitable in the absence of manganese. 6. Method which combines 4 and 5. Precipitate with ammonia (38)> decant, filter, wash, remove the still 102 half-moist precipitate, as far as practicable, from the filter, dissolve the particles still adhering to the latter in nitric acid, transfer this to the dish, to effect also the solution of the bulk of the precipitate ; proceed as in 101, and add the fluid, separated from the sesquioxide of iron and alumina, which still contains small quantities of lime and magnesia, to the principal filtrate. This method is often em- ployed with the best success in my laboratory, in absence of manganese ; the determination of the alumina being effected by estimating first the total amount of sesquioxide of iron and alumina, then the sesquioxide of iron separately by the volumetiical method. A A 354- SEPARATION OF THE BASES. [ 161. Supplement to tJte Fourth Group. To 160 and 161. SEPARATION OF SESQUIOXIDE OF URANIUM FROM THE OXIDES OF GROUPS I. IV. It has already been stated, in 114, that sesquioxide of uranium 103 cannot be completely separated from the alkalies by means of ammonia, as the precipitated ammonio -sesquioxide of uranium is likely to contain also fixed alkalies. This precipitate should there- fore be dissolved in hydrochloric acid, the solution evaporated in a platinum crucible, the residue ignited in a current of hydrogen gas (see Fig. 61, 111), the chloride of the alkali metals extracted with water, and the protoxide of uranium converted, by ignition in the air, into protosesquioxide. From baryta, sesquioxide of uranium may be separated by sul- phuric acid, from strontia and lime, by sulphuric acid and alcohol Ammonia fails to effect complete separation of sesquioxide of uranium from the alkaline earths, the uranium precipitate always containing not inconsiderable quantities of the earths. Sesquioxide of ui-anium is separated from the protoxides of nickel, 104 cobalt, and manganese, oxide of zinc, and magnesia, by means of carbonate of baryta, added in excess to the fluid, which is allowed to stand in the cold for 24 hours, with occasional stirring (62)- From alumina and sesquioxide of iron, sesquioxide of uranium may be separated by either of the following methods : a. Add ammonia to the solution until a precipitate just begins to 105 form, then a sufficient quantity of solution of carbonate of ammonia, which has previously been boiled up once, to destroy any bicarbonate present ; dilute with water, and then filter off from the precipitate, which contains the whole of the alumina and sesquioxide of iron. Heat the filtrate cautiously for some time, then supersaturate with hydrochloric acid, which will redissolve the precipitate formed, and precipitate the uranium finally with ammonia, as directed in 114. If the solution of carbonate of ammonia is too concentrated, or used in too great excess, or contains bicarbonate, sesquioxide of iron passes into the solution, and the experiment turns out a failure (H. Rose}. b. Arendt and Knop ("Chem. Centralbl.," 1857, 163) recommend 106 the following method for the separation of sesquioxide of iron from sesquioxide of uranium : Precipitate the two oxides by ammonia, dissolve in acetic acid, add carbonate of ammonia until a precipitate just begins to form, boil, and filter. The precipitate contains the whole of the iron, and some sesquioxide of uranium, which is re- moved from it by cold digestion with solution of carbonate of ammonia. The same method may be employed also to effect the separation of sesquioxide of uranium from alumina. 162.] SEPARATION OF THE BASES. 355 FIFTH GROUP. OXIDE OF SILVER SUBOXIDE OF MERCURY OXIDE OF MERCURY OXIDE OF LEAD TEROXIDE OF BISMUTH OXIDE OF COPPER OXIDE OF CADMIUM. I. SEPARATION OF THE OXIDES OF THE FIFTH GROUP FROM THOSE OF THE PRECEDING FOUR GROUPS. 162. Index: Oxide of silver from the oxides of groups 1 4, 107, 108. Oxide of mercury from the oxides of groups 1 4, 107, 109. tiuboxide of mercury from the oxides of groups 1 4, 107, 109. Oxide of lead from the oxides of groups 1 4, 107, 110; from groups 1 and 2, and from zinc and nickel, 111 ; from protoxide of manganese, 118. Teroxide of bismuth from the oxides of groups 1 4, 107; from protoxide of manganese, 118. Oxide of copper from the oxides of groups 1 4, 107, 112, 113; from oxide of zinc, 114, '115, 116; from prot- oxide of manganese, 118. Oxide of cadmium from the oxides of groups 1 4, 107; from oxide of zinc, 117; from protoxide of manganese, 118. A. General Method. SEPARATION OF ALL THE OXIDES OF THE FIFTH GROUP FROM THOSE OF THE PRECEDING FOUR GROUPS. Principle : Sulphuretted Hydrogen precipitates from Acid Solutions the Metals of the Fifth Group, but not tJiose of the first Four Groups. The following points require especial attention in the execution 107 of the process : a. To effect the separation of the oxides of the fifth group from those of the first three groups, by means of sulphuretted hydrogen, it is necessary simply that the reaction of the solution should be acid, the nature of the acid to which the reaction is due being of no consequence. But, to effect the separation of the oxides of the fifth group from those of the fourth, the presence of a free mineral acid is indispensable ; otherwise, zinc and, under certain circumstances, also cobalt and nickel may fall down with the sulphides of the fifth group. /3. But even the addition of hydrochloric acid to the fluid will not always entirely prevent the precipitation of the zinc. Rivot and Bouquet (" Anual. d. Chem. u. Pharm.," 80, 384) declare a complete separation of copper from zinc by means of sulphuretted hydrogen, altogether impracticable. Calvert ("Journ. f. prakt. Chem.," 71, 155) states that he has arrived at the same conclusion. On the other hand, Spirgatis ("Journ. f. prakt. Chem.," 58, 351) concurs with H. Rose in declaring that complete separation of copper from zinc may be effected by means of sulphuretted hydrogen, in presence of a sufficient quantity of free acid. AA2 356 SEPARATION OF THE BASES. [ 162. In this conflict of opinions, I deemed it the wiser course to subject this method once more to a searching investigation. I therefore in- structed one of the students in my laboratory, Mr. Grundmann, to make a series of experiments in the matter, with a view to settle the question. See Analytical Notes and Experiments, No. 91. The results obtained proved incontestably that copper may be completely separated from zinc by sulphuretted hydrogen, if the following instructions are strictly complied with. Add to the copper and zinc solution a copious amount of hydro- chloric acid (e.g. to 0'2 grm. of oxide of copper in 25 c.c. of solution, 10 c.c. of hydrochloric acid of I'l sp. gr.), conduct into the fluid sulphuretted hydrogen largely in excess, filter before the excess of sulphuretted hydrogen has had time to escape or become decom- posed, wash with sulphuretted hydrogen water, dry, roast, redissolve in nitrohydrochloric acid, evaporate nearly to dryness, add water and hydrochloric acid as above, and precipitate again with sul- phuretted hydrogen. This second precipitate is free from zinc; it is treated as directed in 119, 1, c. If cadmium is present, a portion of this metal is likely to remain in solution, in presence of the large amount of hydrochloric acid added. It is therefore necessary, in that case, after conducting the sulphu- retted hydrogen gas into the fluid, to add saturated sulphuretted hydrogen water until no more sulphide of cadmium precipitates, and then to proceed as for the separation of copper. The separation, of cadmium from zinc requires accordingly also a double precipi- tation with sulphuretted hydrogen, if the quantity of zinc is any way considerable. However, with proper attention to the instruc- tions here given, the method gives perfectly satisfactory results. y. The other metals of the fifth group comport themselves in this respect the same as cadmium, i.e., they are not completely precipitated by sulphuretted hydrogen in presence of too much free acid in a concentrated solution. Lead requires the least amount of free acid to be partly retained in solution ; then follow in order of succession, cadmium, mercury, bismuth, copper, silver (M. Martin, " Journ. f. prakt. Chem.," 67, 371). The separation of these metals from zinc must, therefore, if necessary, be effected by the same process as that of cadmium from zinc (/3). & If hydrochloric acid produces no precipitate in the solution, it is preferred as acidifying agent ; in the contrary case, sulphuric acid or nitric acid must be used, and the fluid rather largely diluted. B. Special Metliods. SEPARATION OF THE SEVERAL OXIDES OF THE FIFTH GROUP FROM SOME OR ALL OXIDES OF THE FIRST FOUR GROUPS. 1. SILVER is most simply and completely separated from the 108 OXIDES OF THE FIRST FOUR GROUPS by means of hydrochloric acid. The hydrochloric acid must not be used too largely in excess, and the fluid must be sufficiently dilute ; otherwise a portion of the silver will remain in solution. Care must be taken also not to omit the addition of nitric acid, which promotes the separation of the chloride of silver. The latter should, under these circum- stances, be collected and washed on a filter ( 115, 1, a, /3), as wash- ing by decantation would give too large a bulk of fluid. 162.] SEPARATION OF THE BASES. 357 2. The separation of MERCURY from the METALS OF THE FIRST 109 FOUR GROUPS may be effected also by ignition, which will cause the volatilization of the mercury or the mercurial compound, leaving the non-volatile bodies behind. The method is applicable to alloys as well as to oxides, chlorides, and sulphides. Which of these several methods may be the most appropriate, depends upon the nature of the metals from which the mercury is to be separated, and the selection is accordingly guided by the deportment of the respective compounds. The quantity of mercury is -estimated, in this method, either from the loss of weight suffered by the ignited substance, in which case the operation is conducted in a crucible ; or the sublimed mercury is collected and weighed as directed 118, I, a. The best way, where practicable, is to proceed in the manner described in 132 (separation of mercury from silver, A and y) must also be attended here. As regards y, antimony and tin are to be inserted between cadmium and mercury, in the order of metals there given. With respect to the exceptional conditions required to secure the com- plete precipitation of certain metals of the sixth group, I refer to Section IV. I have to remark in addition. a. That sulphuretted hydrogen fails to separate arsenic acid from oxide of zinc, as, even in presence of a large excess of acid, the whole or at least a portion of the zinc precipitates with the arsenic as Zn S, AsS 6 (W older}. To secure the separation of the two bodies in a solution, the arsenic acid must first be converted into arsenious acid, by heating with sulphurous acid, before the sulphu- retted hydrogen is conducted into the fluid. ft. That in presence of antimony, tartaric acid is advantageously * Hydrochloric acid answers best as acidifving agent. 164.] SEPAllATION OF THE BASES. 369 added if oxides of the fourth group alone are present, which may be thrown down from the filtrate, after addition of ammonia, by sulphide of ammonium ; but that it had better be omitted in the ana- lysis of compounds containing alumina, alkaline earths, and alkalies. In the case of such compounds, sulphuretted hydrogen is conducted into the clear hydrochloric acid solution, water is then added, sul- phuretted hydrogen again conducted into the fluid, a further quan- tity of water added, and the precipitation completed by con- ducting a sufficient amount of sulphuretted hydrogen into the fluid. 2. Methods based upon the Solubility of the Sulphides of the Metals of the Sixth Group in Sulphides of the Alkali Metals. a. THE OXIDES OF GROUP VI. (with the exception of Gold and 142 Platinum) FROM THOSE OF GROUP V. Precipitate the acid solution with sulphuretted hydrogen, paying due attention to the directions given in Section IY. under the heads of the several metals, and also to the remarks in 141. The preci- pitate consists of the sulphides of the metals of groups Y. and VI. Wash, treat immediately after with yellow sulphide of ammonium, and digest the mixture for some time at a gentle heat ; filter off the clear fluid, treat the residue again with sulphide of ammonium, digest a short time, repeat the same operation, if necessary, a third and fourth time, filter, and wash the residuary sulphides of group Y. with water containing sulphide of ammonium. If protosulphide of tin is present, some flowers of sulphur must be added to the sulphide of ammonium, unless the latter be very yellow. In pre- sence of copper, the sulphide of which is a little soluble in sulphide of ammonium, sulphide of sodium should be used as solvent. However, this substitution can be made only in the absence of mercury, since the sulphides of that metal are soluble in sulphide of sodium. Add to the alkaline filtrate, gradually! hydrochloric acid in small portions, until the acid predominates ; allow to subside, and then filter the fluid from the precipitate, which consists of the sulphides of the metals of the sixth group, mixed with some sulphur. Schneider ("Aimed, d. Chem. u. Pharm.," 101, 64)states that he failed in effecting complete separation of tersulphide of bismuth from bisul- phide of tin by digestion with sulphide of potassium, but succeeded in accomplishing that object, by conducting sulphuretted hydro- gen into the potassa solution of tartrate of teroxide of bismuth and protoxide of tin (which decompose into suboxide of bismuth and binoxide of tin). b. THE OXIDES OF GROUP VI. (with the exception of Gold and 143 Platinum) FROM THOSE OF GROUPS IV. AND Y. a. Neutralize the solution with ammonia, and add yellow sul- phide of ammonium in excess ; cover the vessel, allow the mixture to digest some time at a moderate heat, and then proceed as in 142- Repeated digestion with fresh quantities of sulphide of ammonium is indispensable. On the filter, you have the sulphides of the metals of groups IV. and Y. Wash with water containing sulphide of ammonium. II. BB 370 SEPARATION OF THE BASES. [ 164s. In presence of nickel, this method offers peculiar difficulties. In presence of copper (and absence of mercury), soda and sulphide of sodium are substituted for ammonia and sulphide of ammonium.* ft. In the analysis of solid compounds (oxides or salts), it is in most cases preferable to fuse the substance with 3 parts of dry carbonate of soda and 3 of sulphur, in a covered porcelain crucible, over a lamp. When the contents are completely fused, and the ex- cess of sulphur is volatilized, the mass is allowed to cool, and then treated with water, which dissolves the sulphur salts of the metals of the sixth group, leaving the sulphides of groups IV. and V. un- dissolved. By this means, even ignited binoxide of tin may be tested for iron, &c., and the amount of the admixture determined (H. Rose). The solution of the sulphur salts is treated as in 142- B. Special Methods. 1. Methods based upon the Insolvtbility of some Metals of the Sixth Group in Adds. a. GOLD FROM METALS OF GROUPS IV. ANT> V. IN ALLOYS. a. Heat the alloy with pure nitric acid, or, according to circum- 144 stances, with hydrochloric acid. The other metals dissolve, the gold is left. The alloy must be reduced to filings, or rolled out into thin sheets. Alloys of gold containing silver or lead, or both, can be analysed by this method only if the quantity of the two latter metals, or of either, amounts to more than 80 per cent., otherwise the silver and lead are not completely dissolved. Alloys of silver and gold containing less than 80 per cent, of silver, are therefore fused together with 3 parts of lead, before they are treated with nitric acid. The residuary gold is weighed ; but its purity must be ascertained, by dissolving in cold dilute nitrohydrochloric acid, not in concentrated hot acid, as chloride of silver also is soluble in the latter. At the Mint Conference held ft Vienna, in 1857, the following pro- cess was agreed upon for the mints in the several states of Germany. Add to 1 part of gold supposed to be present, 2^ parts of pure silver, wrapped up in paper, and introduce into a cupel in which the requisite amount of lead is just fusing.t After the removal of the lead (by absorption), the button of gold and silver is flattened, by hammering or rolling, then ignited, and rolled; then treated first with nitric acid of 1-2 sp. gr., afterwards with nitric acid of 1-3 sp. gr. Lastly, it is washed, ignited, and weighed (" Kunst und * The hitherto universally admitted accuracy of this method has lately been called in question by Bloxam ("Ann. d. Chem. und Pharm.," 83, 204). That chemist found that sulphide of ammonium fails to separate small quantities of bisulphide of tin from large quantities of sulphide of mercury and sulphide of cadmium (1 : 100) ; and that more especially the separation of copper from tin and antimony (also from arsenic) by this method is a failure, as nearly the whole of the tin remains with the copper. On the other hand, however, Mr. Lucius, one of the students in my laboratory, has succeeded in effecting complete separation of copper from tin by means of yellowish sulphide of sodium. But it is indispensable to digest three or four times with sufficiently large quantities of the solvent, as stated in the text. t If the weighed sample, say 0'25 grm., contains 98-92 per cent, of gold, 3 grms. of lead are required; if 92-87 '5, 4 grms. ; if 87'5-75, 5 grms. ; if 75-60, 6 grms. ; if 60-35, 7 grms. ; if less than 35, 8 grms. 164.] SEPARATION OF THE BASES. 371 Gewerbeblatt f. Baiern," 1857, 151; " Cliem. Centralbl.," 1857, 307 ; "Polyt. Centralbl.," 1857, 1151, 1471, 1639). 0. Heat the finely divided (tiled or rolled) alloy in a capacious platinum dish with concentrated pure sulphuric acid until the evolu- tion of gas has ceased, and the sulphuric acid begins to volatilize ; or fus the alloy with bisulphate of potassa (H. Rose). Separate the gold- from the sulphates of the metals, by treating the mass first with cold, finally with boiling water. It is advisable to repeat the operation with the separated gold, and ultimately test the purity of the latter. b. PLATINUM FROM OTHER METALS OF GROUPS IV. AND V., IN ALLOYS. The separation is effected by treating the substance with sulphuric 145 acid or, better still, with bisulphate of potassa ; but not with nitric acid, as platinum in alloys will, under certain circumstances, dis- solve in that acid. 2. Method based upon the Separation of Gold in the metallic state. GOLD FROM ALL OXIDES OF GROUPS I. V., with the exception of OXIDE OF LEAD AND OXIDE OF SILVER. Precipitate the hydrochloric acid solution with oxalic acid as 146 directed 123, b, y, and filter off the gold when it has completely separated. Take care to add a sufficient quantity of hydrochloric acid to prevent oxalates insoluble in water precipitating along with the gold, for want of a solvent. 3. Method based upon tlie Precipitation of Platinum as Potassio- or Ammonio- Bichloride of Platinum. PLATINUM FROM THE OXIDES OF GROUPS IV. AND V., with the exception of LEAD AND SILVER. Precipitate the platinum with chloride of potassium or chloride 147 of ammonium as directed 124, and wash the precipitate thoroughly with spirit of wine. 4. Metlwds based upon the Separation of Oxides insoluble in Nitric Acid. a. TIN FROM METALS OF GROUPS IV. AND V. IN ALLOYS. Treat the finely divided alloy with nitric acid as directed 126, 148 1, a, and filter the solution from the undissolved binoxide of tin. The filtrate contains the other metals as nitrates. (In presence of bismuth, wash first with water containing niti-ic acid.) As binoxide of tin is liable to retain traces of copper, the safest way, in an accurate analysis, is to test it for this admixture, and to determine the amount of it as directed in 143, ft. Brunner ("Journ. f. prakt. Ghem.," 58,446) recommends the following course of proceeding, by which the presence of copper in the tin may be effectively guarded against. Dissolve the alloy in a mixture of 1 part of nitric acid, 4 parts of hydrochloric-acid, and 5 parts of water ; dilute the solution largely with water, and heat gently. Add crystals of carbonate of soda until a distinct precipitate has formed, and boil. (In presence of copper, the precipitate must, 372 SEPARATION OF THE BASES. [ 164. in this operation, change from its original bluish-green to a brown or black tint.) When the fluid has been in ebullition some 10 15 minutes, allow it to" cool, and then add nitric acid, drop by drop, until the reaction is distinctly acid, and the precipitate has, after several hours' digestion, acquired a pure white color. The binoxide of tin thus obtained is free from copper ; but it may contain some iron, which can be removed as directed in 143 Before the biuoxide of tin can be considered pure, it must be tested also for silicic acid, as it frequently retains traces of this sub- stance. To this end, it is fused with 3 4 pai'ts of carbonate of soda and potassa, the fused mass boiled with water, and the solution filtered ; hydrochloric acid is then added to the filtrate, and, should silicic acid separate, the fluid is filtered off from this substance. The tin is then precipitated by sulphuretted hydrogen, and the silicic acid still remaining in the filtrate is determined in the usual way ( 140). If hydrochloric acid has produced a precipitate of silicic acid, the last filtration is effected on the same filter (Kliiltel, " Chem. Centralbl.," 1857, 929). 6. TIN FROM THE OXIDES OF GROUPS I., II., III., AS WELL AS FROM 149 PROTOXIDE OF MANGANESE, OXIDE OF ZINC, PROTOXIDE OF NICKEL, PROTOXIDE OF COBALT, OXIDE OF COPPER, and probably also from some other oxides (Lowenlluil, " Journ. f. prakt. Chem.," GO, 257). Precipitate the hydrochloric acid solution, which must contain the tin. entirely as binoxide (bichloride), as directed 126, 1, b ; and separate the precipitated binoxide of tin from the fluid ; the filtrate contains the other oxides. In the process, attend to the following points : a. Sulphate of soda is generally to be preferred as precipitating agent, where the choice is permitted. /3. When the precipitate of binoxide of tin has subsided, decant the supernatant fluid on to a filter, repeat this operation several times, and then treat the precipitate with a boiling mixture of 1 part of nitric acid of 1-2 sp. gr. and 9 parts of water, before trans- ferring it to the filter for the purpose of completing the washing. The results are very satisfactory. If the binoxide of tin is mixed with other oxides admitting of reduction by ignition in a current of hydrogen, these oxides may also be reduced in this manner, and the metals then treated as in 148- c. ANTIMONY FROM THE METALS OF GROUPS IV. AND V. IN ALLOYS. Proceed as in 148, filter the fluid off from the precipitate, and 150 convert the latter into antimonious acid by ignition ( 125, 2). The results are only approximate, as some teroxide of antimony dissolves. 5. Methods based upon tlie Volatility of many Chlorides or Metals. a. TIN, ANTIMONY, ARSENIC FROM COPPER, SILVER, LEAD, COBALT, NICKEL. Treat the sulphides of the metals in a stream of chlorine, proceed- 151 ing exactly as directed in 132- In presence of antimony, fill the flasks/ and h (Fig. 80) with a solution of tartaric acid in water, 164.] SEPARATION OF THE BASES. 373 mixed with hydrochloric acid. In alloys also, the metals may be separated by this method. The alloy must be very finely divided. Arsenical alloys are only very slowly decomposed in this way. b. BINOXIDE OF TIN, TEROXIDE OP ANTIMONY (AND ALSO ANTI- MONIC, ARSENIOUS, AND ARSENIC ACIDS), FROM ALKALIES AND ALKALINE EARTHS. Mix the solid compound with 5 parts of pure chloride of am- 152 monium in powder, in a porcelain crucible, cover this withaconcave platinum lid, on which some chloride of ammonium is sprinkled, and ignite gently until all chloride of ammonium is driven off; add a fresh portion of that salt to the contents of the crucible, and repeat the operation until the weight of the latter remains constant. In this process, the chlorides of tin, antimony, and arsenic, escape, leaving the chlorides of the alkalies and alkaline earths. The " decomposition by this method proceeds most rapidly with arsenical compounds, less quickly with antimonial compounds, and least so with compounds of tin (H. Rose). c. MERCURY FROM GOLD (in alloys and also in other forms of com- bination). The two metals are separated by ignition, and the mercury is 153 either calculated from the loss or collected and weighed ( 118). 6. Methods based upon the Volatility of Ter -sulphide of Arsenic. THE ACIDS OF ARSENIC FROM SESQUIOXIDE OF IRON (probably 154 also from protoxide of nickel, oxide of zinc, oxide of copper, oxide of lead, &c.) Ebelinen. ' Heat the oxidas in sulphuretted hydrogen, by which process they are completely converted into sulphides. The tersulphide of arsenic volatilizes, leaving the sulphides of the other metals behind. 7. Methods based upon the Conversion of Arsenic and Antimony into Ar senates and Antimonates of the Alkalies. ARSENIC FROM THE METALS AND OXIDES OF GKOUPS II., IV., AND V. a. If the substance contains the arsenic in the form of arsenites 155 or arsenates, it is fused with 3 parts of carbonate of soda and potassa and 1 part of nitrate of potassa ; if an alloy, it is fused with 3 parts of carbonate of soda and 1 part of nitrate of potassa. In either case the residue is boiled with water, and the solution, which contains the arseuates of the alkalies, filtered from the undissolved oxides or carbonates. The arsenic acid is determined in the filtrate as directed 127,2. If the quantity of arsenic is only small, the fusion may be effected in a platinum crucible ; but if more con- siderable, the process must be conducted in a porcelain crucible, as platinum would be injuriously affected by it. In the latter case, bear in mind that the fused mass is contaminated with silicic acid and alumina. b. ARSENIC AND ANTIMONY FROM COPPER AND IRON, especially in ores containing sulphur. Diffuse the very finely pulverized mineral through pure solution of 156 potassa, and conduct chlorine into the fluid (comp. 148, II., 2, b). 374 SEPARATION OF THE BASES. [ 164;. The iron and copper separate as oxides, the solution contains sul- phate, arseuate, and antimonate of potassa (Rivot, Beudant, and Daguin, "Compt. rend.," 1853, 835; "Journ. f. prakt. Chem.," 61, 133). c. ARSENIC AND ANTIMONY FROM COBALT AND NICKEL. Dilute the nitric acid solution with water, udd a large excess of 157 potassa, heat gently, and conduct chlorine into the fluid until the precipitate is black. The solution contains the whole of the arsenic and antimony, the precipitate the nickel and cobalt, in form of sesquioxide (JRivot, Beudant and Daguin, "Compt. rend.," 1853, 835 ; "Journ. f. prakt. Chem.," 61, 133). 8. Method based upon the Separation of Arsenic as Ar senate of , Suboxide of Mercury. ARSENIC ACID FROM THE ALKALIES, ALKALINE EARTHS, OXIDE OF ZINC, PROTOXIDE OF COBALT, PROTOXIDE OF NICKEL, OXIDE OF LEAD, OXIDE OF COPPER, OXIDE OF CADMIUM. Proceed exactly as in the separation of phosphoric acid by mercury 158 ( 134, b, y). The arsenic acid cannot be determined in the in- soluble residue in the way in which the phosphoric acid is deter- mined. Treat the filtrate as directed 135, 1 (H. Rose). 9. Method based upon the Separation of A rsenic as Arsenate of Magnesia and Ammonia. ARSENIC ACID FROM ALUMINA AND THE OXIDES OF GROUP IV. Proceed as directed 135,/ a. Treat the precipitated arsenate 159 of magnesia and ammonia the same way as the precipitated phosphate of magnesia and ammonia (see 135, f, a). 10. Method based upon tlve Separation of Arsenic as Arsenio- Molybdate of Ammonia. ARSENIC ACID FROM ALL OXIDES OF GROUPS I. V. Separate the arsenic acid as directed in 127, 2 b, and treat the 160 filtrate as directed in 135, in. 11. Methodbased upon the Insolubility of Arsenate of Sesquioxide of Iron. ARSENIC ACID FROM THE BASES OF GROUPS I. AND II., AND FROM OXIDE OF ZINC, AND THE PROTOXIDES OF MANGANESE, NICKEL, AND COBALT. Precipitate the arsenic acid, according to circumstances, as directed 161 127, 3, a or b, filter, and determine the bases in the filtrate. 12. Method based upon the Insolubility of Chloride of Silver. SILVER FROM GOLD. Treat the alloy with cold dilute nitrohydrochloric acid, dilute, and 162 filter the solution of the terchloride of gold from the undissolved chloride of silver. This method is applicable only if the alloy con- tains less than 15 per cent, of silver ; for if it contains a larger proportion, the chloride of silver which forms protects the undecom- posed part from the action of the acid. In the same way silver may be separated also from platinum. 165.] SEPARATION OF THE BASES. 375 1 3. Method based upon the Insolubility of certain Sulphates in Water or Spirit of Wine. ARSENIC ACID FROM BARYTA, STRONTIA, LIME, AND OXIDE OP LEAD. Proceed as for the separation of phosphoric acid from the same 163 oxides ( 135, c). The compounds of these bases with arsenious acid are first converted iuto arsenates, before the sulphuric acid is added ; this conversion is effected by heatiug the hydrochloric acid solution with chlorate of potassa. 14. Metliod based upon the Separation of Copper as Subiodide. COPPER FROM ARSENIC AND ANTIMONY. Dissolve in nitric or sulphuric acid, taking care to add the acid 164 only slightly in excess, dilute with water or, in presence of antimony, with water containing tartaric acid, and precipitate the copper as in 113- Arsenic and antimony remain in solution (Flajolot). 15. Method based upon the Separation of Copper as Oxalate. COPPER FROM ARSENIC. Add to the nitric acid solution ammonia until the blue precipitate 165 formed remains undissolved upon further addition of the reagent, then effectfsolution by an excess of oxalate of ammonia. Add, cautiously, hydrochloric or nitric acid to acid reaction, and allow the mix- ture to stand. The copper separates almost completely as oxalate, which is then converted by ignition in the air into oxide. Add ammonia to the filtrate, and precipitate with a few drops of sul- phide of ammonium the minute trace of copper still retained in solution (F. Field, " Chem. Gaz.," 1857, 313). 16. Method based upon the different deportment of the several Metals with Cyanide of Potassium. GOLD FROM LEAD AND BISMUTH. These metals may be separated in solution by cyanide of potassium 166 in the same way in which the separation of mercuiy from lead and bismuth is effected (see 123)- The solution of the double cyanide of gold and potassium is decomposed by boiling with hydrochloric acid, and, after expulsion of the hydrocyanic acid, the gold deter- mined by one of the methods given in 123. II. SEPARATION OF THE OXIDES OF THE SIXTH GROUP FROM EACH OTHER. 165. Index : Platinum from gold, 167 ; from antimony, tin, and arsenic, 168. Gold from platinum, 167 ; from antimony, tin, and arsenic, 168. Tin from gold and platinum, 168 ; from arsenic, 169, 176, 177, 178; from antimony, 171, 175,177; prot- oxide from binoxide of tin, 181. 376 SEPAEATTON OF THE BASES. [ 165. Antimony from gold and platinum, 168 ; from arsenic, 170, 171, 172, 173; from tin, 171, 175, 177 ; ter- oxide of antimony from antimonic acid, 180, 182. Arsenic from gold and platinum, 168 ; from tin, 169, 176, 177, 178; from antimony, 170, 171, 172,173; arsenious acid from arsenic acid, 174, 179, 182. 1 . Method based upon the Precipitation of Platinum as Potassio- bichloride of Platinum. PLATINUM FROM GOLD. Precipitate from the solution of the chlorides of the metals the 167 platinum as directed 124, b, and determine the gold in the filtrate as directed 123, b. 2. Method based upon the Volatility of the CUo rides of the in- ferior Metals. PLATINUM AND GOLD FROM TIN, ANTIMONY, AND ARSENIC. Heat the finely divided alloy or the sulphides in a stream of 168 chlorine gas. Gold and platinum are left, the chlorides of the other metals volatilize (compare 132> 133)- 3. Methods based upon the Volatility of Arsenic and Tersulphide of Arsenic. a. ARSENIC FROM TIN (H. Rose}. Convert into sulphides or into oxides, diy at 212 F., and heat a 169 weighed portion of the dried mass in a bulb-tube, gently at first, but gradually more strongly, conducting a stream of dry sulphu- retted hydrogen gas through the tube during the operation. Sul- phur and tersulphide of arsenic volatilize, sulphide of tin is left. The tersulphide of arsenic is received in a small flask connected with the bulb-tube, in the manner described in 132, which contains dilute solution of ammonia. When upon continued application of heat no further sign of sublimation is observed in the colder part of the tube, drive off the sublimate which has collected in the bulb, allow the tube to cool, and then cut it off above the coating. Divide the separated portion of the tube into pieces, and heat these with solution of soda until the sublimate is dis- solved ; unite the solution with the ammoniacal fluid in the re- ceiver, add hydrochloric acid, then, without filtering, chlorate of potassa, and heat gently until the tersulphide of arsenic is com- pletely dissolved. Filter from the sulphur, and determine the arsenic acid as directed 127, 2. The quantity of tin cannot be calculated at once from the blackish-brown sulphide of tin in the bulb, since this contains more sulphur than corresponds to the for- mula Sn S. It is therefore weighed, and the tin determined in a weighed portion of it, by converting it into binoxide, which is effected by moistening with nitric acid, and ignition ( 126, 1, c). Tin and arsenic in alloys are more conveniently converted into oxides by cautious treatment with nitric acid. If, however, it is wished to convert them into sulphides, this may readily be effected ty heating 1 part of the finely divided alloy with 5 parts of carbonate of soda, and 5 parts of sulphur, in a covered porcelain crucible, 165.] SEPARATION OF THE BASES. 377 until the mass is in a state of calm fusion. It is then allowed to "cool, dissolved iu water, the solution filtered from the sulphide of iron, &c., which may possibly have formed, and the filtrate precipitated with hydrochloric acid. b. ARSENIC FROM ANTIMONY IN ALLOYS. Heat a weighed portion of the finely divided alloy with 2 parts 170 of carbonate of soda and 2 parts of cyanide of potassium in a bulb- tube, through which dry carbonic acid is transmitted; apply a gentle heat at first, but increase this gradually to a high degree of intensity, and 'continue heating until no more arsenic volatilizes. Take care not to inhale the escaping fumes ; the safest way is to insert the hind part of the bulb-tube into a flask, in which the arsenic will sublime. Allow the bulb-tube to cool ; after cooling, treat the contents, first with a mixture of equal parts of spirit of wine and water, then with water, and weigh the residuary antimony. The quantity of the arsenic is calculated from the loss. This method gives only approximate results. The direct fusion of the alloy in a stream of carbonic acid or hydrogen gas, without previous addition of carbonate of soda and cyanide of potassium, would give most inaccurate results, as a large quantity of antimony volatilizes under these circumstances. 4. Methods based upon the insolubility of Antimonate of Soda. a. ANTIMONY FROM TIN AND ARSENIC (H. Rose). Oxidize a weighed sample of the finely divided substance, in a 171 porcelain crucible, with nitric acid of 1 - 4 specific gravity, adding the acid gradually. Dry the mass on the water-bath, transfer to a silver crucible, rinsing the last particles adhering to the porcelain into the silver crucible with solution of soda, dry again, add eight times the bulk of the mass of solid hydrate of soda, and fuse for some time. Allow the mass to cool, and then treat with hot water until the undissolved residue presents the appearance of a fine powder ; dilute with some water, and add alcohol of 0'83 sp. gr. in sufficient quantity to make the proportion of its volume to that of the water as 1 to 3. Allow the mixture to stand for 24 t hours, with frequent stirring ; then filter, transfer the last adhering particles from the crucible to the filter by rinsing with dilute spirit of wine (1 volume of alcohol to 3 volumes of water), and wash the undissolved residue on the filter, first with spirit of wine con- taining 1 volume of alcohol to 2 volumes of water, then with a mixture of equal volumes of alcohol and water, and finally with a mixture of 3 volumes of alcohol and 1 of water. Add to each of the alcoholic fluids used for washing a few drops of solution of car- bonate of soda. Continue the washing until the color of a portion of the fluid running off remains unaltered upon being acidified with hydrochloric acid and mixed with sulphuretted hydrogen water. Rinse the antimouate of soda from the filter, wash the latter with a mixture of hydrochloric acid and tartaric acid, dissolve the anti- monate in this mixture, precipitate with sulphuretted hydrogen, and determine the antimony as directed 125, 1. To the filtrate, which contains the tin and arsenic, add hydro- chloric acid, which produces a precipitate of arsenate of binoxide of tin ; conduct now into the unfiltered fluid s\ilphuretted hydrogen 378 SEPARATION OF THE BASES. [ 165. for some time, allow the mixture to stand at rest until the odor ot that gas has almost completely gone off, and then separate the weighed sulphides of the metals as in 169- If the substance contains only antimony and arsenic, the alcoholic filtrate is heated, with repeated addition of water, until the fluid scarcely retains the odor of alcohol; hydrochloric acid is then added, and the arsenic determined as arsenate of magnesia and ammonia ( 127, 2). b. DETERMINATION OF THE SULPHIDE OF ARSENIC CONTAINED IN THE COMMERCIAL SULPHIDE OF ANTIMONY ( Wackenroder). Deflagrate 20 grammes of the finely pulverized sulphide of auti- 172 mony with 40 grammes of nitrate of potassa and 20 grammes of carbonate of soda, by projecting the mixture gradually into a red- hot hessian crucible ; treat the strongly ignited mass repeatedly with water, filter the solution, acidify the nitrate with hydrochloric acid, treat with sulphurous acid, and precipitate the arsenic with sulphu- retted hydrogen- Digest the moist precipitate, which contains a small admixture of antimony, with carbonate of ammonia, filter, acidify the filtrate, conduct sulphuretted hydrogen into the fluid, and determine the arsenic as tersulphide as directed 127, 4. 5. Methods based upon the Precipitation of Arsenic as Arsenate of Magnesia and Ammonia. a. ARSENIC FROM ANTIMONY. Oxidize the metals or sulphides with nitrohydrochloric acid or 173 hydrochloric acid and chlorate of potassa, or with chlorine in alka- line solution (see 148, II., 2,6) ; add tartaric acid, a large quantity of chloride of ammonium, and then ammonia in excess. Should the addition of the latter reagent produce a precipitate, this is a proof that an insufficient quantity of chloride of ammonium or of tartaric acid has been used, which error must be corrected before proceeding with the analysis. Then precipitate the arsenic acid as directed 127, 2, and determine the antimony in the filtrate as directed 125, 1. As basic tartrate of magnesia might precipitate with the arsenate of magnesia and ammonia, the precipitate should always, after slight washing, be redissolved in hydrochloric acid, and the solution precipitated again with ammonia. b. ARSENIOUS ACID FROM ARSENIC ACID. Mix the solution with a large quantity of chloride of ammonium, 174 precipitate the arsenic acid as directed 127, 2, and determine the arsenious acid in the filtrate by precipitation with sulphuretted hydrogen ( 127, 4). 6. Methods based upon the Precipitation of tlie Metals in the metallic state. a. TIN FROM ANTIMONY (Gay-Lussac). Heat a weighed portion of the finely divided alloy (or other form 175 of combination) with hydrochloric acid, add chlorate of potassa in small portions until the mass is dissolved, and then divide the fluid into two equal parts, a and b. In a pi'ecipitate both nietals on a tin rod, rinse them off, and weigh ; add to b a tolerably 165.] SEPARATION OF THE BASES. 379 amount of hydrochloric acid, introduce a clean slip of tin, and heat fur some time. By this process, the antimony is completely thrown down in form of a black powder, and the bichloride of tin reduced to protochloride. Wash the antimony off the tin with water con- taining hydrochloric acid, collect upon a weighed filter, dry, and weigh. The difference gives the quantity of tin. b. DETERMINATION OF ARSENIC IN METALLIC TIN (Gay-Lussac. " Ann. de Chim. et de Phys.," 23, 228 ; Liebig and Kopp's " An- nual Keport," 1847 and 1848, page 968). Dissolve the laminated or granulated* metal in a mixture of 1 176 equivalent of nitric acid and 9 equivalents of hydrochloric acid, with the aid of a gentle heat. The solution ensues without evolu- tion of gas ; protochloride of tin and chloride of ammonium are formed, the arsenic is left in the form of powder. N0 5 + 9 HC1 + 8 Su = 8 SuCl + NH 4 , 01 + 5HO. The nitro-hydrochloric acid must, therefore, not be used in a much larger proportion than will give to 8 equivalents of metal 1 equivalent of N0 5 , and 9 equivalents of HC1. 7. Method based upon the Precipitation of some of the Metals as /Sulphides by Hyposulphite of Soda. ARSENIC AND ANTIMONY FROM TIN. Mix the solution with hydrochloric acid in excess, heat to boiling, 177 and add hyposulphite of soda until the precipitate appears no longer orange or yellow, but white, and the fluid looks opalescent, owing to the separation of sulphur. Arsenic and antimony are completely precipitated, whilst the whole of the tin remains in solution (Vohl, " Annal. d. Chem. u. Pharm.," 96, 240). If arsenic alone is present in the precipitate, determine the metal as directed 127, 4 ; if antimony alone, as directed 125, 1 ; if both metals are present, separate them according to the instructions of 171 or 173- The tin in the filtrate is estimated best as directed 126, c. 8. Method based upon the Precipitation of Tin as Arsenate of Binoxide of Tin. TIN FROM ARSENIC. Ed. Hd/ely (" Phil. Mag.," x. 220) has proposed the following 178 method of determining both the tin and the arsenic in commercial stannate of soda, which often contains a large admixture of arsenate of soda. Mix a weighed sample with a known quantity of arsenate of soda in excess, add nitric acid also in excess, boil, filter the pre- cipitate, which has the composition 2 Su 2 , As O fi + 10 Aq, and wash ; expel the water by ignition, and weigh the residue, which consists of 2 Sn O 2 , As 6 . In the filtrate determine the excess of arsenic acid as directed 127, 2 or 4. Calculate the amount of binoxide of tin from the weight of the ignited residue ; and that of the arsenic acid from the weight of the latter, joined to the quantity found in the filtrate, after deducting the amount added. 9. Volumetrical Methods. a. ARSENIOUS FROM ARSENIC ACID. * Prepared by pouring the fused metal into water. 380 SEPARATION OF THE BASES. [ 165. Convert the whole of the arsenic in a portion of the substance 179 into arsenic acid and determine the total amount of this as directed 127, 2; determine in another portion the arsenious acid as directed 127, 5, a or b, and calculate the arsenic acid from the difference. b. TEROXIDE OF ANTIMONY FROM ANTIMONIC ACID. Determine in a sample of the substance the total amount of the 180 antimony as directed 125, 1, in another portion that of the ter- oxide as directed 125, 3, and calculate the antimonic acid from the difference. 10. Methods based upon the Indirect Gravimetric Determina- tion of one of the Oxides. a. PROTOXIDE OF TIN IN PRESENCE OF BINOXIDE. Determine in a portion of the substance the total quantity of the 181 tin ; dissolve another portion in hydrochloric acid, taking care to exclude the air, and drop the solution into a large excess of solu- tion of chloride of mercury, with stirring. Treat the precipitated subchloride of mercury as directed 117, 1. One equivalent (Hg, Cl) corresponds to 1 equivalent of protochloride of tin (Sn Cl) (U. Rose). b. ARSENIOUS ACID IN PRESENCE OF ARSENIC ACID; TEROXIDE OF ANTIMONY IN PRESENCE OF ANTIMONIC ACID. Determine in a portion of the substance the total quantity of the 182 arsenic ; dissolve another portion in hydrochloric acid (of course, no oxidizing agents, such as nitrates, &c., must be present), and add an excess of solution of sodio- or ammonio-terchloride of gold. Let the mixture stand several days (properly protected from dust), in the cold, or, in the case of dilute solutions, at a gentle heat; filter the fluid from the separated gold, and determine the latter as directed 123, b. Keep the filtrate to see whether an additional quantity of gold may not separate, which is sometimes the case. 2 equivalents of gold correspond to 3 equivalents of arsenious acid (2 Au Cl s + 3 As Cl s = 3 As Cl s + 2 Au). The same method may be employed also to determine teroxide of antimony in presence of antimonic acid ; however, in the case of antimony, a larger excess of hydrochloric acid must be added, to effectively prevent the pre- cipitation of antimonic acid. The gold should be washed with water containing hydrochloric acid (H. Rose). II. THE SEPARATION OF THE ACIDS FROM EACH OTHER. I have again to remark that the methods of separation given in the following paragraphs proceed generally upon the assumption that the acids exist either in the free state, or in combination with alkaline bases. Compare the introductory remarks on the subject, 151. Where several acids are present in one and the same sub- stance, the analysis is often effected by determining one acid in one portion, the other in another portion. Of course, the methods here^ given do not embrace every imaginable case, but only the most important cases, and those of most frequent occurrence. 166.] SEPARATION OP THE ACIDS. 331 FIRST GROUP. ARSENIOUS ACID ARSENIC ACID CHROMIC ACID SULPHURIC ACID PHOSPHORIC ACID BORACIC ACID OXALIC ACID HYDROFLUORIC ACID SILICIC ACID CARBONIC ACID. 166. 1. ARSENIOUS ACID AND ARSENIC ACID FROM ALL OTHER ACIDS. Precipitate the arsenic from the solution by means of sulphu- 183 retted hydrogen ( 127, 4), filter, and determine the other acids in the filtrate. If chromic acid is present, this is reduced, before the addition of the sulphuretted hydrogen, by one of the methods given in 130; as sulphur would fall down with the tersulphide of arsenic if this precaution were neglected. If arsenic acid is present the fluid is heated to 158 F., which. greatly facilitates its precipitation ; or the acid is reduced to arsenious acid, by means of sulphurous acid, before adding the sul- phuretted hydrogen. From those acids which form soluble salts with magnesia, arsenic acid may be separated also by precipitation as arsenate of magnesia and ammonia as directed 127, 2. 2. SULPHURIC ACID FROM THE OTHER ACIDS. a. From tlie Acids of Arsenic, from Phosphoric, Boracic, Hydro- fluoric, Oxalic, Silicic, and Carbonic Acids. Acidify the dilute solution strongly with hydrochloric acid, mix 184 with chloride of barium, and filter the sulphate of baryta from the solution, which contains all the other acids. Determine the sul- phate of baryta as directed 132. 6. From Hydrofluoric Add in Insoluble Compounds. A mixture of sulphate of baryta and fluoride of calcium cannot 185 be decomposed by simple treatment with hydrochloric acid; the insoluble residue always contains, besides sulphate of baryta, sulphate of lime and fluoride of barium. The object in view may be attained, however, by the following process : Fuse the substance with 6 parts of carbonate of soda and potassa, and 2 parts of silicic acid ; allow the mass to cool, treat with water, and add carbonate of ammonia to the solution obtained ; filter, wash the separated silicic acid with dilute solution of carbonate of ammonia, supersaturate the filtrate with hydrochloric acid, and precipitate with chloride of barium. If you wish to determine the fluorine also, acidify with nitric acid, precipitate with nitrate of baryta, then saturate with carbonate of soda, and precipitate the fluoride of barium by spirit of wine. Wash a long time, first with spirit of wine of 50 per cent., then with strong alcohol ; dry, ignite, and weigh. The insoluble residue left upon treating with water contains the baryta and lime. Dissolve in hydrochloric acid, filter from the undissolved silicic acid, and determine the bases in the filtrate as directed 154 (//. Rose). c. In Presence of a large proportion of Chromic Acid. Reduce the chromic acid by boiling the dry compound with 186 concentrated hydrochloric acid (if this process is conducted accord- 382 SEPARATION OF THE ACIDS. [ 166. ing to the directions of 130, I., d, ft, it gives, at the same time, the quantity of the chromic acid) ; dilute the solution largely, and precipitate, first the sulphuric acid by adding a small excess of chloride of barium, then the excess of baryta by sulphuric acid, and lastly the sesquioxide of chromium by ammonia. d. From Hydrofluosilicic A cid. Precipitate the hydrofluosilicic acid as directed 133, then the 187 sulphuric acid in the filtrate by baryta. 3. PHOSPHORIC ACID FROM THE OTHER ACIDS. a. From the acids of arsenic, see 183 ; from sulphuric acid, see 184- b. From Chromic Acid. Precipitate the phosphoric acid as phosphate of magnesia and 188 ammonia ( 134, b). Determine the chromic acid in the filtrate as directed 130, a, ft, b, c, or d. c. From Boracic Acid. Precipitate the phosphoric acid as in 188, and determine the 189 boracic acid in the filtrate as directed 136, II., b. d. From Oxalic Acid. a. If the two acids are to be determined in one and the same sample 190 of the substance, the aqueous solution is mixed with sodio-terchlo- ride of gold in excess, heat applied, and the quantity of oxalic acid present calculated from that of the reduced gold ( 137, c, a). The gold added in excess is separated from the filtrate by means of sul- phuretted hydrogen, and the phosphoric acid then precipitated by sulphate of magnesia. If the compound is insoluble in water, hydrochloric acid is used as solvent, and the process conducted as directed 137, c, ft. ft. If there is a sufficient quantity of disposable substance, the 191 oxalic acid is determined in one portion according to the directions of 137, b, or d, and the phosphoric acid in another portion. If the substance is soluble in water, and the quantity of oxalic acid inconsiderable, the phosphoric acid may be precipitated at once with sulphate of magnesia, chloride of ammonium, and ammonia: if not, the substance is ignited with carbonate of soda and potassa, which destroys the oxalic acid, and the phosphoric acid is deter- mined in the residue. e. Phosphates from Fluorides. a. The substance is soluble in water. aa. If the substance contains a relatively large quantity of 192 fluorine, which will permit the estimation of the latter from the difference, precipitate the solution by chloride of cal- cium, wash, dry, ignite, and weigh. The residue consists of phosphate of lime and fluoride of calcium. Heat in a platinum vessel, with sulphuric acid, until all the fluorine has escaped as hydrofluoric acid, taking care not to raise the heat to a degree at which sulphuric acid volatilizes ; then determine the lime and the phosphoric acid as directed 135, c. By de- 166.] SEPARATION OF THE ACIDS. 383 ducting the phosphoric acid and lime from the total weight of the precipitate, the fluorine is found by the following calcula- tion : The eq. of the fluorine less the eq. of the oxygen : the eq. of the fluorine the ascertained loss of weight : the fluorine sought. 66. If the substance contains a relatively small proportion 193 of fluorine, mix the solution with basic nitrate of suboxide of mercury. A yellow precipitate of basic phosphate of suboxide of mercury is produced, the fluoride of mercury remaining in solution. Determine the phosphoric acid in the precipitate as directed 134, 6, y. Neutralize the filtrate with carbonate of soda, conduct sulphuretted hydrogen into the unfiltered fluid, then filter, aud determine the fluorine as directed 138, I. (H. Hose). ft. The substance is not soluble in water, but decomposed by acids (e. g., Apatite, Bone-ash). Dissolve in hydrochloric acid, evaporate with sulphuric acid, as 194 in 192? until the fluorine is completely expelled, and determine in the residue the phosphoric acid on the one part, the oxides on the other. Now, if you know the proportion between the phosphoric acid and the bases in the analysed compound, you may readily calculate the expelled fluorine by the excess of the bases, the oxygen of the latter being equivalent to the fluorine. y. Tlie substance is insoluble in water and not decomposed by acids. Fuse with carbonate of soda and silicic acid as in 185, treat the 195 fused mass with water, and the solution with carbonate of ammonia. You have now in solution the whole of the fluorine and phosphoric acid in combination with an alkali (H. Rose), and may accordingly proceed as in 192 or 193. 4. FLUORIDES FROM BORATES. Mix the solution assumed to contain borate and fluoride of an 196 alkali metal with some carbonate of soda, and add chloride of calcium in excess. A precipitate is formed, which contains the whole of the fluorine or fluoride of calcium, and besides this, car- bonate and some borate of lime ; the greater proportion of the latter having been redissolved by the excess of the liine salt added. Determine the fluoride of calcium in the precipitate as directed in 138, I. The small quantity of boracic acid in the precipitate is, in this process, partly volatilized, partly dissolved, after evaporating he mass with acetic acid and extracting with water. It is therefore necessary to determine the boracic acid in a separate portion of the substance ; this is effected according to the directions of 136, 2 (A. Stromeyer, " Jonrn. f. prakt.' Chern.," 100, 91). 5. FLUORIDES FROM SILICIC ACID AND SILICATES. y A great many native silicates contain fluorides ; care must, there- fore, always be taken, in the analysis of minerals, not to overlook the latter. If the silicates containing fluoride are decomposable by acids 384 SEPARATION OP THE ACIDS, [ 166. (which is only rarely the case) and the silicic acid is separated, in the usual way, by evaporation, the whole of the fluorine may vola- tilize. a. Berzdiugs method. Fuse the elutriated substance with 4 parts of carbonate of soda, 197 for some time, at a strong red heat ; digest the mass in water, boil, filter, and wash, first with boiling water, then with solution of carbonate of ammonia. The filtrate contains all the fluorine as fluoride of sodium, and, besides this, carbonate of soda, silicate of soda, and aluminate of soda. Mix the filtrate with carbonate of ammonia and heat the mixture, replacing the carbonate of ammonia which evaporates. Filter off the precipitate of hydrate of silicic acid and hydrate of alumina, and wash with carbonate of ammonia. Heat the filtrate until the carbonate of ammonia is completely ex- pelled, and determine the fluorine as directed 1 38. To separate the silicic acid, decompose the two precipitates with hydrochloric acid as directed 140, II., a* /3. Wohlers method (suitable only for the analysis of substances 198 which contain a large proportion of fluorine and are readily decom- posed by sulphuric acid). Keduce the compound under examination to the very finest powder, introduce this into a small flask, pour pui-e sulphuric acid over it, close the flask quickly with a perforated cork into which a small tube with chloride of calcium is fitted, weigh the apparatus with the greatest despatch, and then apply heat until the evolution of fumes of fluoride of silicon (Si Fl a ) ceases ; remove the last re- maining traces of the gas from the flask, by an exhausting syringe, let the apparatus cool, and then weigh. The loss indicates the weight of the fluoride of silicon expelled in the process. Deduce from this the quantity both of the fluorine and of the silicon, cal- culate the latter as silicic acid, and add the quantity found to the weight of the silicic acid in the residue. 6. FLUORIDES, SILICATES, AND PHOSPHATES, IN PRESENCE OF EACH OTHER. Native compounds of fluorides, silicates, and phosphates are not 199 uncommon. They are decomposed as in 197. Complete decompo- sition of the phosphates is not always effected in this process, as phosphate of lime, for instance, is only partially decomposed by fusion with carbonate of soda. The solution remaining after the separation and removal of the silicic acid and the volatilization of the carbonate of ammonia, contains in presence of phosphates besides fluoride of sodium and carbonate of soda, also phosphate of soda. Neutralize the fluid nearly with hydrochloric acid, precipitate with chloride of calcium, filter, dry, and ignite the precipitate, which consists of fluoride of calcium, phosphate of lime, and car- bonate of lime ; treat the residue with acetic acid in excess, and evaporate on the water-bath to dryness and complete expulsion of * The whole of the silicic acid may be removed from the filtrate by treating with carbonate of ammonia : addition of carbonate of z : .nc and ammonia, as recommended by Berzelius, and afterwards by Regnault, appears therefore superfluous (H. Rose). 166.] SEPARATION OF THE ACIDS. 385 the acetic acid ; treat the acetate of lime, into which the carbonate has been converted by the last operation, with water, weigh the residue, which consists of phosphate of lime and fluoride of cal- cium, and effect its ulterior decomposition as directed in 192- I n the original residue of the first operation and in the precipitate thrown down by carbonate of ammonia, determine the silicic acid, the rest of the phosphoric acid, and the bases. 7. SILICIC ACID FROM ALL OTHER ACIDS. a. In Compounds which are decomposed by Hydrochloric Acid. Decompose the substance by digestion with hydrochloric acid or 200 nitric acid, evaporate on the water-bath* to dryness ( 140, II., a.), and treat the residue, accor-diug to circumstances, with water, hydro- chloric acid, or nitric acid ; filter the fluid from the residuary silicic acid, and determine the other acids in the filtrate. In presence of boracic acid, or fluorine, this method is inapplicable, and the process described in b (201) is employed instead. If carbonates are present, the carbonic acid is determined in a separate portion of the substance. b. In Compounds which are not decomposed by Hydrocldoric Acid. Decompose the substance by ignition with cai-bonate of soda and 201 potassa ( 140, II., b, a.), and either treat the residue at once cau- tiously with dilute hydrochloric or nitric acid, and the solution thus obtained as in a (200) > r treat the residue with water, pre- cipitate the silicic acid from the solution by heating with bicar- bonate of ammonia, filter, add the precipitate to the undissolved residue, and determine the silicic acid, in the united mass, by treat- ing with hydrochloric acid, and proceeding as directed 140, II., a. Determine the other acids in the filtrate. Which of these two methods may be preferable in particular cases, depends upon the nature of the bases, and upon the relative proportion which the silicic acid bears to the latter. In presence of boracic acid and fluorine, the latter method alone is applicable. 8. CARBONIC ACID FROM ALL OTHER ACIDS. When carbonates are heated with stronger acids, the carbonic 202 acid is expelled ; the presence of carbonates, therefore, does not interfere with the quantitative estimation of most other acids. And as, on the other hand, the carbonic acid is determined by the loss of weight or by combination of the expelled acid, the presence of salts of non-volatile acids does not interfere with the determination of the carbonic acid. Accordingly, compounds containing carbonates, sulphates, phosphates, &c., are analysed in two separate portions, the carbonic acid being determined in one, the other acids in the other sample. In presence of fluorides, one of the weak non-volatile acids, such as tartaric acid or citric acid, must be employed to expel the carbonic acid ; since, were sulphuric acid or hydrochloric acid used for the purpose, part of the liberated hydrofluoric acid would escape with the carbonic acid. The pro- cess described in 139, II., e, fi, may be employed, without modifica- tion, in presence of fluorides. If, as will occasionally happen in * A higher temperature would not answer. II. C C 3S6 SEPAEATION OF THE ACIDS. [ 167. an analysis, a mixed precipitate of fluoride of calcium and carbo- nate of lime is thrown down from a solution, the two salts may be separated by evaporating the mixed precipitate with acetic acid to dryness, and treating the residue with water : the acetate of lime formed from the carbonate is dissolved, the fluoride of calcium is left undissolved. SECOND GROUP. HYDROCHLORIC ACID HYDROBROMIC ACID HYDRIODIC ACID HYDROCYANIC ACID HYDROSULPHURIC ACID. I. SEPARATION OF THE ACIDS OF THE SECOXD GROUP FROM THOSE OF THE FlRST. 167. a. Separation of all tfie Acids of the Second Group from those of the First. Mix the dilute solution of the compound under examination with 203 nitric acid, add solution of nitrate of silver in excess, and filter the fluid from the insoluble chloride, bromide, iodide, and then precipitate, after addition of nitric acid, with nitrate , of silver (//. Hose). 4. CHLORIDES IN PRESENCE OP FLUORIDES. If the substance is sohible in water, the separation may be 208 effected as directed in 203 ; but it is more convenient to precipi- tate the fluorine with nitrate of lime, and the chlorine in the filtrate with solution of nitrate of silver. Insoluble compounds are fused with carbonate of soda and silicic acid (see 185)- 5. CHLORINE IN PRESENCE OF FLUORINE, IN SILICATES. Proceed as directed 197- Saturate the alkaline filtrate nearly 209 with nitric acid, precipitate with nitrate of lime, separate the fluo- ride of calcium and the carbonate of lime as directed in 202, and pre- cipitate the chlorine in the filtrate by solution of nitrate of silver. 6. SULPHIDES IN SILICATES. If the substance is decomposed by acids, reduce it to the very 210 finest powder, and treat with fuming nitric acid ( 148, II., 2, a). When the sulphur is completely oxidized, dilute, filter off the silicic acid, add carbonate of ammonia to the filtrate, to remove the portion of silicic acid which may possibly have dissolved, filter again, and determine in the filtrate the sulphuric acid formed. If the substance is not decomposed by acids, fuse with 4 parts of car- bonate of soda and 1 part of nitrate of potassa, boil the fused mass with water, filter, remove the dissolved silicic acid from the filtrate by carbonate of ammonia (185). filter again, and determine in the filtrate the sulphuric acid produced from the sulphur. c c 2 388 SEPARATION OP THE ACIDS. [ 168, 169. Supplement. ANALYSIS OF COMPOUNDS CONTAINING SULPHIDES OF THE ALKALI METALS, CARBONATES, SULPHATES, AND HYPOSULPHITES. 168. The following method was first employed by G. Wertlier (" Journ. 211 f. prakt Chem.," 55, 22), in the examination of gunpowder residues. Put the substance into a flask, pour over it water, in which a sufficient quantity of carbonate of oxide of cadmium* is suspended; insert the cork, and shake the vessel frequently. The sulphide of the alkali metal decomposes completely with the carbonate of cad- mium. Filter the yellowish precipitate off, and treat with dilute acetic acid (not with hydrochloric acid) ; the carbonate of cadmium dissolves, the sulphide of cadmium is left undissolved. Oxidize the latter with chlorate of potassa and nitric acid ( 148, II., 2, a, ft), and precipitate with chloride of barium the sulphuric acid formed from the sulphide. Heat the fluid filtered from the yellow precipitate, and mix with solution of neutral nitrate of silver. The precipitate thrown down by that reagent consists of cai-bonate of silver and sulphide of silver (K O, S 2 O 2 + Ag O, N O 5 = K S O s + Ag S + N O 6 ). Remove the former salt by means of ammonia, and precipitate from theammoniacal solution the silver after acidifying with nitric acid by means of chloride of sodium. Each equivalent of chloride of silver so obtained corresponds to an equivalent of carbonate, t Dissolve the sulphide of silver in dilute boiling nitric acid, determine the silver in the solution as chloride of silver, and calculate from the result the quantity of the hyposulphite ; 1 equivalent of Ag Cl corresponds to 2 equivalents of sulphur in hyposulphurous acid, and accordingly to 1 equivalent of hyposulphite (K O, S 2 O S ). From the fluid filtered from the sulphide and carbonate of silver, remove first the excess of silver by means of hydrochloric acid, and then precipitate the sulphuric acid by a salt of baryta. From the weight of the sulphuric acid found you have, of course, to deduct an amount corresponding to the quantity of that acid resulting from the decomposition of the hyposulphurous acid, and accordingly for 1 equivalent of chloride of silver formed from the sulphide, 0'28 eq. of sulphuric acid. The difference gives the amount of sulphuric acid originally present in the analysed compound. By way of control, you may determine, in the fluid filtered off from the sulphate of baryta, the alkali as sulphate as directed in 97 or 98. II. SEPARATION OF THE ACIDS OF THE SECOND GROUP FROM EACH OTHER. 169. 1. CHLORINE FROM BROMINE. All the methods of direct analysis hitherto proposed to effect the 212 * To obtain the carbonate of oxide of cadmium free from alkali, carbonate of ammonia must be used as precipitant. t A quantity equivalent to the sulphide found has to be deducted from this (K S + Cd 0, CO f = CdS + KO, CO,). * 169.] SEPARATION OF THE ACIDS. 389 separation of chlorine from bromine are defective. The bromine is therefore usually determined in a more indirect way. a. Precipitate with nitrate of silver, wash the precipitate, dry, fuse, and weigh. Transfer an aliquot part of the mixed chloride and bromide of silver to the bulb of a weighed bulb-tube,* fuse in the bulb, let the mass cool, and weigh. This operation gives both the total weight of the tube with its contents, and the weight of the portion of mixed chloride and bromide of silver in the bulb. The greatest accuracy in the several weighings is indispensable. Now transmit through the tube a slow stream of dry pure chlorine gas, heat the contents of the bulb to fusion, and shake the fused mass occasionally about in the bulb. After the lapse of about 20 minutes, take off the tube, allow it to cool, hold it in an oblique position, that the chlorine gas may be replaced by atmospheric air, and then \\eigh. Heat once more, for about 10 minutes, in a sti'eam of chlorine gas, and weigh again. If the two last weighings agree, the experiment is terminated ; if not, the operation must be repealed once more. The loss of weight suffered, multiplied by 4-223 gives the quantity of the bromide of silver decomposed by the chlorine. For the mode of calculating the results, see 200. The mixed chloride and bromide of silver may also be heated in a cur- rent of chlorine gas, instead of in a bulb-tube, in a small porcelain- boat inserted into a glass tube. This method gives very accurate results if the proportion of bromine present is not too small ; but most uncertain results in cases where mere traces of bromine have to be determined in presence of large quantities of chlorides, as, for instance, in saline springs. To render the method available in such cases, the great point is to produce a silver compound containing all the bromine, and only a small part of the chlorine. This end may be attained in several ways. a. Feldings method (" Journ. f. prakt. Chem.," 45, 269). Mix the solution cold with a quantity of solution of nitrate of silver 213 not nearly sufficient to effect complete precipitation, shake the mixture vigorously, and leave the precipitate for some time in the fluid, with repeated shaking. If the amount of the precipitate produced corresponds at all to the quantity of bromine present, the whole of the latter substance is obtained in the precipitate. Felding recommends the following proportions : To 0-001 of bromine use ^ or \ the quantity of solution of nitrate of silver that would be required to effect complete precipitation ; to 0-0001 of bromine, T V ; to 0-00002 of bromin, 3 V ; to O'OOOOl of bromiue, -$. Wash the mixed precipitate of chloride and bromide of silver thoroughly, dry, ignite, weigh, and treat with chlorine, as above. To find the quantity of the chlorine, precipitate another weighed portion of the original solution completely with solution of nitrate of silver, and deduct from the weight of the precipitate the quan- tity of bromide of silver found. * The best way of effecting the transfer of this portion from the crucible to the tube is to fuse the mass in the crucible again, and then let a portion of it run from the latter into the tube. 390 SEPARATION OF THE ACIDS. [ 169. /3. Marchand (" Journ. prakt. Chein.," 47, 363) has slightly 214 modified FeUing's method. He reduces with zinc the mixed pre- cipitate of chloride aud bromide of silver obtained by Fehling's fractional precipitation, decomposes the solution of chloride and bromide of zinc with carbonate of soda, evaporates to dryness, and treats the residue with absolute alcohol, which dissolves all the bromide of sodium with only a little of the chloride of sodium ; he then evaporates the solution to dryness, treats the residue with water, precipitates again with solution of nitrate of silver, and sub- iects a part of the weighed precipitate to the treatment with chlorine. y. If a fluid containing chlorides in presence of some bromide, is 215 heated, in a distillation flask, with hydrochloric acid and binoxide of manganese, the whole of the bromine passes over before any of the chlorine. Upon this circumstance, Mohr (Annal. d. Chem. u. Pharrn., 93, 80) bases the folio wing method for effecting the concentration of bromine. Distil as stated, and conduct the vapors, through a double-bent tube, into a wide WovZfs bottle, which contains some strong solution of ammonia. Dense fumes form in the bottle, filling it gradually. Conduct the excess of vapors from the first into a second bottle, with narrow neck, which contains ammoniated water. Both bottles must be sufficiently large to allow no vapors to escape. When the whole of the bromine is evolved, which may be distinctly seen by the color of the space above the liquid in the distillation flask and tubes, raise the cork, to prevent the receding of bromide of ammo- nium fumes. Let the apparatus cool, and unite the contents of the 2 bottles ; the fluid contains the whole of the bromine, and a relatively small portion of the chlorine. b. Instead of treating the mixed chloride and bromide of silver 216 in a current of chlorine as in a, it may also be reduced to metallic silver, in a current of hydrogen. After accurately determining the weight of the reduced metal, calculate the amount of chloride of silver equivalent to it, subtract from this the weight of the chloride and bromide of silver subjected to the reducing process, and multiply the difference by 4-223, as in a (212). Wackenroder. It will be seen that one and the same portion of mixed bromide and chloride of silver may be treated first as directed in a (212)> then, by way of control, as directed in b. The difference found in the direct way in the first, and by calculation in the second ex- periment, between the weight of the mixed chloride and bromide of silver and the amoiiht of chloride of silver equivalent to it, must be the same. c. Fr. Molir (" Annal. d. Chem. u. Pharm.," 93, 76) recommends 217 to precipitate by a known quantity of silver the bromine and part of the chlorine, and to weigh the mixed precipitate of chloride and bromide of silver; which will of course again furnish the same bases for calculation as in b (216)- The known quantity of silver used as precipitant is either weighed in the direct way, and dissolved in nitric acid, or added in form of a solution of nitrate of silver of known strength. This method is more convenient than the process described in a (212) ; hut I do not consider it quite so accurate, more particularly for small quantities of bromine. It presupposes 169.] SEPARATION OF THE ACIDS. 891 that a weighed quantity of silver will give an absolutely correspond- ing amount of chloride of silver, which practically is not the case, errors to the extent of some milligrammes being scarcely avoidable ; it may accordingly happen that bromine is calculated from the supposed difference, even in cases where there is absolutely none present. Now the method a (212) is not so liable to lead to such mistakes, at least not to the same extent. On the contrary, a simple experiment will show that pure chloride of silver, heated cautiously, in a bulb-tube or porcelain boat, in a current of chlorine, suffers no alteration of weight ; an error occurring in this operation to the extent of ^ milligramme is less excusable than one to the extent of 2 milligrammes, arising in the conversion of 2 or 3 grammes of silver into chloride, more especially if a filter is required in the process ; and this can hardly ever be dispensed with in a partial precipitation, as, in such cases, the precipitate always subsides less readily and completely than in cases of full and complete pre- cipitation. d. Pisanfs method (" Compfc. rend.," 44, 352 ; " Journ. f. prakt. 218 Chem.," 72, 266) may be looked upon as a modification of c (217). That chemist recommends to add a known quantity of solution of nitrate of silver in slight excess, filter, and determine the silver in the filtrate by iodide of starch (139)- The precipitate is weighed as in c. This method precludes the partial precipitation. e. Determine in a portion of the solution the chlorine + bromine 219 (by precipitating with solution of nitrate of silver), either gravi- metrically or volumetrically; in another portion the bromine, either by the colorimetric method ( 143, I., b), or by the volumetrical method ( 143, I., c). Calculate the chlorine from the difference. This method is very suitable for an expeditious analysis of mother- liquors. 2. CHLORINE FROM IODINE. a. Mix the solution with nitrate of protoxide of palladium, and 220 determine the precipitated protiodide of palladium as directed 145, I, b. Conduct sulphuretted hydrogen into the filtrate, to remove excess of the palladium, destroy the excess of sulphuretted hydrogen by solution of sulphate of sesquioxide of iron, and precipitate the chlorine finally with solution of nitrate of silver. It is generally found more simple and convenient to divide the solution into two parts, and precipitate from one portion the iodine, by means of pro tochlo ride of palladium, as directed 145, I., b, from the other portion, the chlorine and iodine jointly with solution of nitrate of silver, and to calculate the chlorine from the difference. If you have no solution of nitrate of protoxide of palladium ready, and the chlorine aiid iodine must be determined jointly in a portion of the solution under examination, add a measured quantity of a solution of protochloride of palladium, determine the amount of chlorine in this in another exactly equal portion of the same solution, and deduct this. The results are accurate. In the case of fluids containing a large proportion of chlorides of the alkali metals, to a small quantity of iodides of the alkali metals, the iodide is concentrated by adding carbonate of soda to the fluid, evaporating to dryness, treating the residue with alcohol, 392 SEPARATION OF THE ACIDS. [ 169. evaporating the alcoholic solution, with addition of a drop of solution of soda, and treating the residue with water. b. Precipitate a portion of the fluid with solution of nitrate of 221 silver, and determine the chlorine + iodine ; in another portion, determine the quantity of the iodine separately by the voluiuetrical method ( 115, I., d, or e); calculate the chlorine from the dif- ference. c. Proceed exactly as for the indirect determination of bromine 222 in presence of chlorine (212)- The loss of weight suffered by the silver precipitate in the fusion in chlorine gas, multiplied by 2'569, gives the quantity of the iodide of silver decomposed by chlorine. The methods described in 216, 217, and 218, may also be employed. The results obtained by these methods in the case of chlorine and iodine are still more accurate than in the case of chlorine and bromine, as the difference between the equivalents of iodine and chlorine is much greater than between those of chlorine and bromine. d. Mot-ides Metlwd ("Compt. rend.," 35, 789 ; " Jonrn. f. prakt. 223> Chem.," 58, 317). Free iodine dissolves in benzole, imparting a red color to the fluid ; this color is the darker, the greater the quantity of iodine dissolved ; upon exposure to the air, the iodine volatilizes, and the fluid loses its color. If, therefore, a fluid containing an iodide of an alkali metal is mixed with a few drops of red fuming nitric acid and 2 or 3 grammes of benzole, and the mixture vigorously shaken, the benzole ascends to the surface, exhibiting a magnificent color. To determine the quantity of the iodine, the iodized benzole is washed with water, sulphurous acid added, drop by drop, with shaking, until the fluid is decolorized ; then solution of nitrate of silver, the precipitate digested with nitric acid, the iodide of silver washed with alcohol, and determined in the usual way. Chlorine imparts no color to benzole, and remains dissolved in the water with which the benzole is washed. It is precipitated with solution of nitrate of silver. e. The separation of iodine from chlorine may be effected also by 224 means of bisulphide of carbon (or chloroform), as follows : Mix the solution with a few drops of a solution of hyponitric acid in sul- phuric acid, or with a few drops of red fuming nitric acid, add 4 or 5 grammes of bisulphide of carbon, shake vigorously, and sepa- rate the violet-colored bisulphide of carbon, by careful decautation, from the fluid, which contains the chlorine (and bromine). Wash carefully by decantation, then add dilute chlorine water, drop by drop, with shaking, until the color just disappears, which is a sign that the whole of the iodine is converted into I C1 5 . Separate the solution from the bisulphide of carbon, add solution of iodide of potassium in sufficient excess, and determine the liberated iodine as directed 146, 1 or 3. Six parts of the iodine found correspond to 1 part of iodine originally present. If yon wish to avoid the decautation and washing of the bisulphide of carbon, transfer the fluid, mixed with chlorine water to decolorization, to a rather narrow graduated cylinder, note the volume of the solution of the pentachloride of iodine (after deduction of the bisulphide of carbon), take out a por- tion with the pipette, and treat this as directed. The results which 109.] SEPARATION OF THE ACIDS. 393 I obtained by this process were satisfactory. The method is par- ticularly suitable for the estimation of small quantities of iodine. f. Add to the solution of the iodide and chloride \ c.c. of solu- 225 tion of iodide of starch of known strength (139), then, drop by drop, with stirring, decimal standard solution of nitrate of silver (see 115, at the end), until the iodide of starch is decolorized. The amount of silver solution used (after deducting the small quan- tity required for the decolorization of the ^ c.c. of iodide of starch, solution added, and which must be separately determined) cor- responds exactly to the amount of iodine in the analysed compound ; for iodide of starch is decolorized before the precipitation of chlo- rine begins. To determine now the chlorine also, add again solution of nitrate of silver in slight excess, filter, and determine the excess of silver in the filtrate by means of iodide of starch (139)- Deduct the amount of solution of nitrate of silver corresponding to the ^c.c. of iodide of starch solution added, and to the iodine present, as well as the excess of silver solution from the total quan- tity added, and calculate the chlorine from the difference. This method is expeditious ; the results are accurate (Pisani, " Compt. rend.," 44, 352 ; " Journ. f. prakt. Chem.," 72, 266). Compare also Analytical Notes and Experiments, No. 92. 3. CHLORINE, BROMINE, AND IODINE FROM EACH OTHER.* a. The three metalloids are determined jointly in a portion of 226 the fluid, by precipitating with solution of nitrate of silver. To determine the iodine, another portion is precipitated with proto- chloride of palladium in the least possible excess. The fluid filtered from the precipitate is freed from palladium by means of sulphu- retted hydrogen, and the excess of the latter removed by means of sulphate of sesquioxide of iron ; the chlorine and bromine are then precipitated jointly, either completely or partially, with solution of nitrate of silver, and the bromine is finally determined as directed 169, 1. If the compound contains a large proportion of chlorine to a small proportion of bromine, the iodine may be precipitated also by nitrate of protoxide of palladium, as there is no danger, in that case, of protobromide of palladium being thrown down with the pre- cipitate. The filtrate is treated as above. These methods give very accurate results ; but they are applicable only if the quantity of iodide present is somewhat considerable. b. Remove the iodine from the solution by bisulphide of carbon, 227 or chloroform, as in 224 ; but, in order to be quite sure that no bromine is liberated, use hyponitric acid, free from nitric acid.t (Grange, " Compt. rend.," 33, 627 ; " Journ. f. prakt. Chem.," 55, 167). In the fluid separated from the iodized bisulphide of carbon, determine the chloi'iue and bromine as directed in 169, 1, and in the iodized bisulphide of carbon, the iodine as in 224- This method is particularly recommended for the separation of small quantities of iodine, and in this respect is supplementary to 226- * The method recently recommended by Fr. Field ("Chem. Gaz.," 1857, No. 357), for the separation of chlorine, iodine, and bromine, rests on a false basis, as iodide of silver is sufficiently soluble in iodide of potassium solution, and bromide of silver in bromide of potassium solution, to give rise to very considerable mistakes. t This may be obtained by a more intense ignition of feebly ignited nitrate of oxide of lead. 394 SEPARATION OF THE ACIDS. [ 169. c. Determine in a portion of the compound the chlorine, bi'omine, 223 and iodine jointly by precipitation with nitrate of silver. Deter- mine the silver in the weighed precipitate as in 216- Or add a known quantity of solution of nitrate of silver in slight excess, filter, and determine the small excess of silver in the nitrate by means of iodide of starch (218)- Determine the iodine separately by Dupre's method (see below), calculate the quantity of iodide of silver and of silver corresponding to the amount of iodine found, deduct the calculated amount of iodide of silver from the mixed iodide, chloride, and bromide of silver, that of the silver from the known quantity of the metal contained in the mixed compound ; the difference gives the joint amount of chloride and bromide of silver, on the one, the quantity of the metal contained in the bromide and chloride, on the other hand, and, accordingly, the basis for calculating the chlorine and bromine (216)- As regards the estimation of iodine in presence of bromides, A. and F. Dupre found that, if the solution of an iodide contains 1 part of bromide of potassium, or more, in 1500 parts of water, protobromide of iodine (I Br) is formed upon addition of chlorine water ; if the solution contains less than 1 part of bromide of potassium in 1500 parts of water, higher bromides in varying pro- portions are formed in addition to the protobromide. If the solution contains only 1 part of bromide of potassium to 13,000 parts of water, pentabromide of iodine (I Br 6 ) alone is formed. If the iodine was dissolved in bisulphide of carbon, the conversion into I Br is marked simply by the change of the violet color of the fluid to yellowish brown (Zirconium color), whereas the formation of I Br s is marked by the change of violet to white. Upon these reactions A. and F. Dupre have based the following method : Test the fluid first by adding bisulphide of carbon, then, gradually, chlorine water, to see whether the color will change from violet to white. If this is not the case, dilute to the required degree, and, to make quite sui'e, add one-half more water ; then proceed as directed 145, I., d, a or/3. A. and F. Dupre obtained most satis- factory results by this process ; the method is particularly recom- mended for the determination of small quantities of iodine. d. Proceed generally as in c (228), l>"t determine the iodine by 229 Pisanis method (225)- This method also gives very satisfactory results. Presence of bromides does not interfere with the accuracy of the estimation of the iodine (Analytical Notes and Experi- ments, No. 93). 4. ANALYSIS OF IODINE CONTAINING CHLORINE. a. Dissolve a weighed quantity of the dried iodine in cold sul- 230 phurous acid, precipitate with solution of nitrate of silver, digest the precipitate with nitric acid, to remove the sulphite of silver which may have precipitated along with the iodide and chloride, and then determine the weight of the precipitated silver salt. The calculation of the iodine and chlorine is made by the following equations, in which A represents the quantity of iodine analysed, x the iodine contained in it, y the chlorine contained in it, and B the .amount of chloride and iodide of silver obtained : 169.] SEPARATION OF THE ACIDS. 395 x + y = A, and Aq + I Aq+Cl JL r- x+ But as and the result is -1-851 A b. If you have free iodine and free chlorine in solution, determine 231 in a portion, after heating with sulphurous acid, the iodine as iodide of palladium ( 145, L, b), and treat another portion as directed 146, 1. Deduct from the apparent amount of iodine found by the latter process, the actual quantity calculated from the iodide of palladium ; the difference expresses the amount of iodine equivalent to the chlorine contained in the analysed compound. 5. ANALYSIS OP BROMINE CONTAINING CHLORINE. a. Proceed exactly as in 230> weighing the bromine in a small 232 glass tube. Taking A to be equal to the analysed bromine, B to the bromide and chloride of silver obtained, x to the bromine contained in A, y to the chlorine contained in A, the calculation is made by the following equations : x + y = A and -2-35 A b. Mix the weighed anhydrous bromine with solution of iodide 233 of potassium in excess, and determine the separated iodine as directed 146, 1. From these data, the respective quantities of bromine and chlo- rine are calculated by the following equations. Let A represent the weighed bromine, i the iodine found, y the chlorine found in A, x the bromine contained in A, then i- 1-58664 Bunsen, the originator of methods 4 and 5, has proved their perfect accuracy by a series of successful experiments (" Arinal d. Chem. u. Pharm.," 86, 274, 276). 6. CYANOGEN FROM CHLORINE, BROMINE, OR IODINE. a. Precipitate with solution of nitrate of silver, collect the pre- 234 cipitate upon a weighed filter, and dry on the water-bath until the weight remains constant ; then determine the cyanogen by the 396 SEPARATION OF THE ACIDS. [ 170. method of organic analysis j the difference expresses the quantity of the chlorine, bromine, or iodine. b. Precipitate with solution of nitrate of silver as in a, dry the 235 precipitate at 212 F., and weigh. Heat the precipitate, or an ali- quot part of it, in a porcelain crucible, with cautious agitation of the contents, to complete fusion ; add dilute sulphuric acid to the fused mass, then reduce by zinc, filter the solution off" from the metallic silver and paracyanide of silver, and determine the chlorine, iodine, and bromine in the filtrate, in the usual way by solution of nitrate of silver. Neubauer and Kerner (" Annal. d. Cheni. u. Pharm.," 101, 344) obtained very satisfactory results by this method. c. Determine the elements jointly in a portion of the solution, 236 by precipitating with solution of nitrate of silver, and the cyanogen in another portion, by the volumetrical method ( 147, I., b or c). 7. FERRO- OR FERRI-CYANOGEN FROM HYDROCHLORIC ACID. To analyse ferro- or ferri-cyanide of potassium, &c., mixed with 237 the chloride of an alkali metal, determine in one portion the ferro- or ferri-cyanogen as directed 147, III. ; acidify another portion with nitric acid, precipitate with solution of nitrate of silver, filter, wash the precipitate, fuse with 4 parts of carbonate of soda, and 1 part of nitrate of potassa, extract the fused mass with water, and deter- mine the chlorine in the solution as directed in 141. 8. SULPHURETTED HYDROGEN FROM HYDROCHLORIC ACID. The usual method of separating the two acids by means of a 238 metallic salt is liable to give false results, as part of the chloride of the metal may fall down with the sulphide. The safest way, there- fore, is to precipitate both as silver compounds, dry the precipitate at 212 F., and determine the sulphur in a weighed portion ; or, which is usually preferred, determine in a portion of the solution the sulphuretted hydrogen as directed 148, in another portion the sulphur + chlorine in form of silver salts. To remove sul- phuretted hydrogen from an acid solution, in order that chlorine may be determined in the latter by means of nitrate of silver, H. Rose recommends to add solution of sulphate of sesquioxide of iron, which will effect the separation of sulphur alone ; the separated sulphur is allowed to deposit, and then filtered off. THIRD GROUP. NITRIC ACID CHLORIC ACID. I. SEPARATION OF THE ACIDS OF THE THIRD GROUP FROM THOSE OF THE FIRST TWO GROUPS. 170. a. If you have a mixture of nitric acid or chloric acid with 239 another free acid in a fluid containing no bases, determine in one portion the joint amount of the free acid, by the acidimetrical method (see Special Part), in another portion the acid mixed with the chloric or nitric acid, and calculate the amount of either of the lutter from the difference. 170.] SEPARATION OF THE ACIDS. 397 b. If you have to analyse a mixture of a nitrate or chlorate with 240 some other salt, determine in one portion the nitric acid or chloric acid by the volumetrical method ( 149, II., a, and 150), or the nitric acid by means of arsenious acid (149, II., 6); and in another portion the other acid. I think I need hardly remark that no sub- stances must be present which would interfere with the application of these methods. c. From the chlorides of those metals which form with phos- 241 phoric acid insoluble tribasic phosphates, the salts of the acids of the third group may be separated also by digesting the solution with recently precipitated thoroughly washed tribasic phosphate of silver, and boiling the mixture. In this process, the chlorides transpose with the phosphate chloride of silver and phosphate of the metal with which the chlorine was originally combined being formed, which both separate, together with the excess of the phosphate of silver, whilst the chlorates and nitrates remain in solution (Chevenix; Lassaigne, "Journ. de Pharm.," 16, 289; " Pharm. Centralbl.," 1850, 121). d. The estimation of the chloric acid in a chlorate, in presence of 242 the chloride of an alkali metal, may be effected also in the following manner : A weighed portion of the compound is precipitated from the aqueous solution with nitrate of silver, and the precipitated chloride of silver accurately weighed ; an equal portion of the sub- stance is cautiously ignited, the residue dissolved in water, nitrate of silver added in excess to the solution, and the precipitated chloride of silver weighed. The quantity of the chloric acid is then calcu- lated from the difference in the weight of the two precipitates. II. SEPARATION OF THE ACIDS or THE THIRD GROUP FROM EACH OTHER. We have as yet no method to effect the direct separation of nitric 243 acid from chloric acid ; the only practicable way, therefore, is to de- termine the two acids jointly in a portion of the compound, either by the method given 149, II., a, a, or by 149, II., b ; and in another portion the chloric acid, by adding carbonate of soda in excess, evaporating to dryness, fusing the residue until the chlorate is com- pletely converted into chloride, and then determining the chlorine in the latter ; 1 equivalent of chloride of silver produced from this corresponds to 1 equivalent of chloric acid, provided there was no chlorine originally present. 398 ORGANIC ANALYSIS. [ 171. SECTION VI. ELEMENTARY OE ULTIMATE ANALYSIS OF ORGANIC BODIES. 171. ORGANIC compounds contain only comparatively few of the ele- ments which constitute the material world. A small number of them consist simply of 2 elements, viz., C and H; the greater number contain 3 elements, viz., usually, C, H, and O; most of the rest 4 elements, viz., generally, C, H, 0,andN; a small number 5 elements, viz., C, H, O, N, and S; and a few, 6 elements, viz., C, H, O, N, S, and P (?). This applies to all the natural organic compounds which have as yet come under our notice. But we may artificially prepare organic com- pounds containing other elements besides those enumerated ; thus we know many organic substances, the radicals of which contain chlorine, iodine, or bromine ; or arsenic, antimony, tin, zinc, platinum, iron, cobalt, &c., oxide of copper ;t then fill the combustion tube up to b (see Fig. 96) with oxide of copper, either using the tube itself to take up the oxide with, or transferring the latter from the crucible to the tube with the aid of a small warm copper funnel and a teaspoon of German silver. Transfer a portion of the oxide of copper from the tube to the mortar, add the substance intended for analysis from the small tube in which it has been weighed, taking care to shake out, as far as practicable, the last adhering particles of the substance ; put by the empty small tube carefully, as you will have to re-weigh it. Mix the substance and the oxide in the mortar most intimately together, taking care to avoid a too energetic pressure upon the pestle ; add to the mixture nearl\ all the oxide of copper still in the tube, leaving only a layer of about 3 or 4 centimetres in the latter and mix the whole most intimately together. Take the pestle out of the mortar, shaking off as clean as possible the minute particles of the mixture adhering to it ; transfer the greatest part of the contents of the mortar to the tube, employing the latter itself for the purpose ; place the rest of the mixture on a smooth card, and pass it from this into the tube ; rinse the mortar with a little more oxide of copper from the crucible, and put this also into the tube, which will now be full to about a (Fig. 96) ; fill up to within 3 or 4 centimetres from the mouth with pure oxide of copper from the crucible, and close the tube temporarily with a dry cork. The reason why the operation of filling the tube is conducted over the sheet of glazed paper is that, should any of the mixture be spilled, this may be readily recovered.^ c. A few gentle taps on the table will generally suffice to shake together the contents of the tube, so as to completely clear the pointed end from oxide of copper, and leave a free passage for the evolved gases from end to end, as shown by the shading in the cut. Should this fail, as will occasionally happen, owing to malformation of the beak, the * Care must be taken that no particles of the substance adhere to the sides of the tube, at least not at the top. f The oxide which has served for this purpose is put by. J In Mulder's laboratory, I saw the operation of filling performed in a different, but certainly very easy and expeditious way. The combustion tube was placed upright in a retort holder, and the mixture, which had been made in a small copper dish, filled in through a smooth, warm copper funnel. 175.] ORGANIC ANALYSIS. 409 object in view may be attained by striking the mouth of the tube several times against the side of a table. Place the tube now into the wooden trough D (Fig. 97), connect it by a cork with the chloride of calcium tube B, and the latter again with an exhausting syringe. Surround the combustion tube in its whole length with hot sand (I., 15), Fig. 97. and pump out the air slowly (quick and incautious pumping might cause a portion of the mixture to pass into the chloride of calcium tube). Open the stopcock a, to admit a fresh supply of air, which is completely dried in its passage through the chkride of calcium tube ; exhaust again, re- admit fresh air, and repeat this process of alternate exhaustion and re- admission of air 10 or 12 times, which will ensure the perfect removal of the moisture which the oxide of copper may have absorbed during the operation of mixing. d. Connect the end b of the weighed chloride of calcium tube (I., 5) with the combustion tube by means of a dried perforated cork (I., 7) ; lay the furnace upon its supports, with a slight inclination forward, and place the combustion tube in it; connect the end of the chloride of calcium tube, by means of a vulcanized india-rubber tube (I., 6), with the end m of the potassa-apparatus, and, if necessary, secure the connection with silk cord, taking care to press the balls of the two thumbs close together whilst tightening the cords, since otherwise, should one of the cords happen to give way, the whole apparatus might be broken. Rest the potassa-apparatus upon a folded piece of cloth. Fig. 98 shows the whole arrangement. e. To ascertain whether the joinings of the apparatus fit air-tight, put 410 ORGANIC ANALYSIS. [ 175. a piece of wood about the thickness of a finger (s), or a cork or other body of the kind, under the bulb r of the potassa-apparatus, so as to raise that bulb slightly (see Fig. 98). Heat the bulb m, by holding a piece of red-hot charcoal near it, until a certain amount of air is expelled through the apparatus ; then remove the piece of wood (s), and allow the bulb m to cool The solution of potassa will now rise into the bulb m, filling it Fig. 98. more or less ; if the liquid in m preserves, for the space of a few minutes, the same level which it has assumed after the perfect cooling of the bulb, the joinings may be considered perfect ; should the fluid, on the other hand, gradually regain its original level in both limbs of the apparatus, this is a positive proof that the joinings are not air-tight. The few minutes which elapse between the two observations, may be advantageously employed in re-weighing the little tube in which the substance intended for analysis was originally weighed. f. Arrange the position of the combustion tube in the furnace, so as to make the tube project a full inch beyond the latter ; suspend the single screen over the anterior end of the furnace, as a protection to the cork ; put the double screen over the combustion tube about two inches farther on (see Fig. 98), replace the little piece of wood (s) under r, and put small pieces of red-hot charcoal first under that portion of the tube which is separated by the screen ; surround this portion gradually altogether with ignited charcoal, and let it get red-hot ; then shift the screen an inch farther back, surround the newly exposed portion of the tube also with ignited charcoal, and let it get red-hot ; shift the screen another inch farther back, surround with ignited charcoal, and proceed in this manner slowly and gradually extending the application of heat to the pointed end of the tube, taking care to wajt always until the last exposed portion is red-hot before shifting the screen, and also to maintain the whole of the exposed portion of the tube ebefore the screen in a state of ignition, and the projecting part of it so hot that the fingers can hardly bear the shortest contact with it. The whole process requires generally from ^ to 1 hour. It is quite superfluous, and even injudicious, to fan the charcoal during the operation; this should be done only when the process is drawing to an end, as we shall immediately have occasion to notice. The liquid in the potassa-apparatus is gradually displaced from the bulb m upon the application of heat to the anterior portions of the com- bustion tube, owing simply to the expansion of the heated air. When the heat reaches that portion of oxide of copper which has been used to rinse the mortar, a little carbonic acid and aqueous vapor are evolved, which drive out the whole of the air in the apparatus, and force it in large bubbles through the potassa-apparatus. The evolution of carbonic acid and aqueous vapor proceeds with greater briskness when 175.] ORGANIC ANALYSIS* 411 the heat begins to reach the actual mixture ; the first bubbles are only partly absorbed in the potassa-apparatus, as the carbonic acid contains still an admixture of air; but those which follow are so completely ab- sorbed by the potassa, that a solitary air-bubble only escapes from time to time through the liquid. The process should be conducted in a manner to make the gas-bubbles follow each other at intervals of from ^ to 1 second. Fig. 99 shows the proper level of the solution of potassa, during the operation. It will be seen from this that an air- bubble entering at a passes first into the bulb b, thence to c, from c to d, and passing over the solution in the latter, escapes finally into the bulb/ through the fluid which just covers the mouth of the tube e. g. When the tube is in its whole length surrounded with red-hot charcoal, and the evolution of gas has relaxed, fan the burning charcoal gently with a piece of pasteboard. When the evolution of gas has entirely ceased, adjust the position of the potassa- apparatus to a level, remove the charcoal from the farther end of the tube, and place the screen before the point. The ensuing cooling of the tube on the one hand, and the absorption of the carbonic acid in the potassa-apparatus on the other, cause the solu- tion of potassa in the latter to recede, slowly at first, but with increased rapidity from the moment the liquid reaches the bulb m. If you have taken care to adjust the position of the potassa-apparatus correctly, you need not fear that the contents of the latter will recede to the chloride of calcium tube. When the bulb m is about half filled with solu- tion of potassa, break off the point of the combustion tube with a pair of pliers or scissors, whereupon the fluid in the potassa-apparatus will immediately resume its level Restore the potassa-apparatus now again to its original oblique position, invert the glass tube mentioned 174, 10, over the pointed end, supporting it against the arm of a filtering stand; join the suction-tube ( 174, 9), or a caoutchouc-tube, to the potassa-apparatus, and apply suction until the last bubbles no longer diminish in size in passing through the latter. Fig. 100 shows the arrangement of the apparatus at this juncture- This terminates the analytical process. Disconnect the potassa-apra- Fig. 99. Fig. 100. 412 ORGANIC ANALYSIS. [ 176. ratus and remove the chloride of calcium tube, together with the cork, which must not be charred, from the combustion tube ; remove the cork also from the chloride of calcium tube, and place the latter upright, with the bulb upwards. After the lapse of half an hour, weigh the potassa-apparatus and the chloride of calcium tube, and then calculate the results obtained. They are generally very satisfactory ; as regards the carbon, they are nearly absolutely accurate, rather somewhat too low (about 0-1 per cent.) than too high. The method, indeed, is not alto- gether free from sources of error ; but none of these intei'fere materially with the accuracy of the results, and the deficiency arising from the one is partially balanced by the excess arising from the other. In the first place, the air which passes through the solution of potassa dui'ing the combustion, and finally during the process of suction, carries away with it a minute amount of moisture. The loss arising from this cause is in- creased if the evolution of gas proceeds very briskly, since this tends to heat the solution of potassa ; and also if nitrogen gas or oxygen gas passes through the potassa-apparatus (compare 178 and 183); this may be remedied, however, by fixing to the exit end of the latter a weighed tube with solid hydrate of potassa. In the second place, traces of carbonic acid from the atmosphere are carried into the potassa-appa- ratus in the final process of suction ; this may be remedied by connect- ing the pointed end of the combustion tube, during the operation, with a potassa tube, by means of a perforated cork. In the third place, it happens frequently, in the analysis of substances containing a consider- able proportion of water or of hydrogen, that the carbonic acid is not absolutely dried in passing through the chloride of calcium tube ; this may be remedied by fixing behind the chloride of calcium tube, a tube filled with asbestos moistened with sulphuric acid. As regards the hydrogen, the results are somewhat too high, on an average about O'l to 0-15 per cent. ; this arises principally from the cir- cumstance that the air passing through the apparatus during the final process of suction conveys a little moisture into the chloride of calcium tube ; but this may be readily remedied by connecting the pointed end of the combustion tube with a potassa tube. I must, however, expressly remark that, in most cases, it is perfectly superfluous to make the operation more complicated for the purpose simply of correcting these defects, more particularly as we know from innumerable experiments the exact limits of the influence which they may exercise upon the accuracy of the results. 2. Bunseris Modification of Liebig's method (Kolbe, " Handworter- buch der Chemie," Supplemente, 186, A. Strecker, Ibid., 2nd edition, I, 852). 176. The essential points of this modification are, that the oxide of copper is allowed to cool in a closed tube or flask, and that, instead of being mixed with the substance in a mortar, it is transferred at once to the combustion tube, and the operation of mixing effected in the latter, by which means the absorption of moisture from the air is effec- tually guarded against, and the application of the exhausting syringe dispensed with. This modified process is more particularly suitable for the analysis of 176.] ORGANIC ANALYSIS. 413 highly hygroscopic bodies and substances which cannot well be mixed with warm oxide of copper without risk of decomposition. The dried substance is weighed in a tube of thin glass, about 20 centi- metres long, and of about 7 centimetres diameter ; one end of this tube is closed by fusion, the other, during the operation of weighing, with a small smooth cork. Besides this weighing tube, Bunsents method requires, like Liebigs, a combustion tube, potassa-apparatus, chloride of cal- cium tube, connecting tube of vulcanized india-rubber, perfo- rated cork, suction tube, furnace, and oxide of copper (see 174) ; and, in addition to these, a glass filiing tube, or flask (fig. 101), in which the freshly ignited oxide of copper is allowed to cool, and from which it is transferred to the combus- tion tube, secure from the possible absorption of moisture from the air. The freshly ignited and still quite hot oxide of copper is trans- ferred direct from the crucible to this filling tube, or flask, which is then closed air-tight with a cork. It saves time to fill in at once a sufficient quantity of oxide to last for several analyses. Fig. 101. If the cork fits tight, the contents will remain several days fit for use, even though a portion has been taken out, and the tube repeatedly opened. . The filling of the combustion tube is effected as follows : The per- fectly dry tube is rinsed with some oxide of copper ; a layer of oxide of copper, about 10 centimetres long, is introduced into the posterior end of the combustion tube, by inserting the latter into the filling tube or flask containing the oxide of copper (Fig. 102), holding both tubes in an oblique direction, and giving a few gentle taps. Fig. 102. The tube with the substance intended for analysis has been accurately weighed shortly before, together with the cork. After removing the cork cautiously, to prevent the slightest loss of substance, the open end of the tube is inserted as deep as possible into the combustion tube, and the requisite quantity of substance poured from it, by giving it a few turns, pressing it all the while gently against the upper side of the com- bustion tube, to prevent its coining into contact with the powder already poured out ; the two tubes are, in this manipulation, held inclined a little downwards (See Fig. 103). Fig. 103. When a sufficient quantity of the substance intended for analysis has been thus transferred from the weighing to the combustion tube, the latter is restored to the horizontal position, which gives to the former a gentle inclination with the closed end downwards. If the little tube is 414 ORGANIC ANALYSIS. [ 177. now slowly withdrawn, with a few tarns, the powder near the border of the opening falls back into it, leaving the opening free for the cork. The tube is then immediately corked and weighed, the combustion tube also being meanwhile kept closed with a cork. The difference between the two weighings shows the quantity of substance transferred from the weighing to the combustion tube. The latter is then again opened, and a quantity of oxide of copper, equal to the first, transferred to it from the filling tube, or flask, taking care to rinse down with this also the particles of the substance still adhering to the sides of the tube There are now in. the hind part of the tube two layers of oxide of copper, each about ten centimetres long, and with the substance intended for analysis between them. The next operation is the mixing ; this is performed with the aid of a long clean iron wire, with a ring for a handle at one end, and pointed and twisted corkscrew fashion (with a single twist) at the other (see Fig. 104). Fig. 104. The wire is pushed down to the end, and rapidly moved about in all directions. A few minutes suffice to effect perfect intermixture ; so perfect, indeed, in the case of pulverulent substances which do not cake, that the minutest particles can no longer be distinguished with the naked eye. The combustion is effected as in 175. . Difficultly conibustible non-volatile bodies, as, e. g., many resin ou* and extractive matters, coal, &c. If substances of the kind are analysed by the methods given in 175 and 176, minute particles of carbon are liable to escape combustion. To prevent this, one of the following methods is resorted to : 1. COMBUSTION WITH CHROMATE OP LEAD, OR WITH CHROMATE OF LEAD AND BICHROMATE OF POTASSA. 177. Of the apparatus, &c., enumerated in 174, only those marked from 1 to 12 are required, and in addition to these some chromate of lead (S 66, 2). A narrow combustion tube may be selected, as chromate of lead contains a much larger amount of available oxygen in an equal volume than oxide of copper. A quantity of the chromate, more than sufficient to fill the combustion tube, is heated in a platinum or porcelain dish over a gas or Berzelius lamp, until it begins to turn brown ; before filling it into the tube, it is allowed to cool down to 212 F. ; and even below. The process is conducted as the one described in 175, with the single difference that the application of the exhausting syringe is omitted, as chromate of lead is not hygroscopic like oxide of copper. One of the principal advantages which chromate of lead has over oxide of copper as an oxidizing agent, being its property of fusing at a proper heat, the temperature must, in the last stage of the process of combustion, be raised (by fanning the charcoal, &c.) sufficiently high to fuse the contents of the tube completely as far as the layer of the 178.] ORGANIC ANALYSIS. 415 substance extends. To heat the anterior end of the tube to the same degree of intensity would be injudicious, since the chromate of lead in that part would thereby lose all porosity, and thus also the power of effecting the combustion of the products of decomposition which may have escaped oxidation in the other parts of the tube. As the chromate of lead, even in powder, is, on account of its den- sity, by no means all that could be desired in this latter respect, it is preferable to fill the anterior part of the tube, instead of with chromate of lead, with coarsely pulverized oxide of copper, deprived of its hygro- scopic properties by very intense ignition ; or with copper turnings which have been superficially oxidized by ignition in a crucible with access of air. In the case of very difficultly combustible substances e. g., graphites it is desirable that the mass should not alone readily cake, but also, in the last stage of the process, give out a little more oxygen than is given out by chromate of lead. It is therefore advisable in such cases to add to the latter one-tenth of its weight of bichromate of potassa in powder (pulverized after previous fusion). With the aid of this addition, com- plete oxidation of even very difficultly combustible bodies may be effected (Liebig)* 2. COMBUSTION WITH OXIDE OF COPPER AND CHLORATE OB PERCHLO- BATE OF POTASSA. 178. This method requires the whole of the apparatus, &c., enumerated in 174 or 176, and in addition a small quantity of chlorate of potassa. The latter substance is freed from water by heating to the point of fusion, allowing to cool, and then reducing to coarse powder, which is kept in a warm place until required for use. The process is conducted as in 175 or 176, with this difference, that the layer of oxide of copper in the posterior end of the tube is made about 5 centimetres long, instead of 3 or 4, and is mixed with about one-eighth (3 or 4 grins.) of chlorate of potassa ; a layer of 2 centi- metres of pure oxide of copper is placed between this mixture and that which contains the substance to be analysed. When, in the subsequent heating of the tube, you approach the part occupied by the mixture con- taining the chloride of potassa, do nat fail to place the hot charcoal with the greatest caution, so as to ensure the very gradual decomposition of the chlorate ; since, if you neglect this precaution, the impetuous rush of the gas will eject a small portion of the solution of potassa, thus vitiating the analysis altogether. The oxygen liberated from the chlorate of potassa drives the carbonic acid before it, effects the combustion of the unconsumed particles of carbon, and oxidizes the reduced copper. Oxygen gas can therefore escape through the potassa-apparatus only when all. that is oxidizable in the tube has been oxidized. If in the last stage of the process of combustion, a large quantity of gas has in this way passed unabsorbed through the potassa-apparatus, it is unnecessary to break off the point, and draw air through the com- bustion tube, as the latter contains now only oxygen, and no longer * Mayer has lately published a series of most successful experiments made with this excellent method (" Annal. d. Chem. u. Pharm.," 95, 204). 416 ORGANIC ANALYSIS. [ 179. carbonic acid nor aqueous vapour. But through the chloride of calcium tube and the potassa-apparatus, air* must be drawn, as these parts of the apparatus would otherwise be weighed full of oxygen. Chlorate of potassa decomposes with a certain degree of violence which is not the case with perchlorate of potassa. The latter salt, pre- pared by heating the former, may therefore be used instead of it, in the process of combustion, as Buiisen has proposed. The fused and still hot perchlorate is introduced into the farther end of the tube, a loose plug of recently ignited asbestos is inserted, and the tube then filled in the usual way. If Bunsens mode of mixing ( 176) is adopted, perchlorate must always be used in this method instead of chlorate of potassa. As the dry oxygen gas passing through the potassa-apparatus carries away a little aqueous vapor from the solution of potassa, it is advisable to connect the exit tube of the apparatus by a cork, or a tube of vul- canized india-rubber, with a small tube filled with hydrate of potassa, which is afterwards weighed together with the potassa-apparatus ; the increase of weight of the two is equal to the quantity of the carbonic acid absorbed. 3. COMBUSTION WITH OXIDE OP COPPER AND OXYGEN GAS. 179. Many chemists deviate, in the analysis of organic bodies, from the methods described in the preceding paragraphs, and effect the combus- tion with oxide of copper and oxygen gas, supplied by a gasometer. Hess, Dumas and Stass, Erdniann and Marchand, fVohler, and others, have proposed methods based upon this principle, which they employ not only for the analysis of difficultly combustible bodies, but also to effect the determination of the carbon and hydrogen in organic substances in general. As these methods require a gasometer filled with oxygen, also certain arrangements to dry the oxygen completely, and to free it from carbonic acid, it is evident that the apparatus must be more complicated than that of Liebig, or Bunsen. The application of these new methods is therefore generally resorted to in cases where a number of ultimate analyses have to be made in succession ; and also more particularly in the analysis of substances which cannot be reduced to powder, and do not admit therefore of intimate mixture with the oxide of copper. Hess, and Erdmann and MarcJiand use spirit of wine to heat the com- bustion tube. In English laboratories gas is frequently employed for the purpose ;t or red-hot charcoal may be used, with the combustion fur- nace illustrated by fig. 93. Fig. 105 shows Ness's apparatus, with spirit of wine as the source of heat. The nature of the fuel used as source of heat is without influence on the operation ; the accuracy of the results also remains the same with the different sources of heat employed, pi'ovided, of course, that the heat may be regulated at will and carried to a proper degree of intensity. a. In Ness's apparatus (Fig. 105), aa is a trough half filled with spirit of wine, which, in proportion as it burns, is replaced from the bottle C, through a tube opening below the level of the spirit of wine ; bb are wick-holders made of tin, which contain broad flat wicks. They * Air dried and freed from carbonic acid answers the purpose best, t See Hofmann's gas-furnace, page 448. 179.] ORGANIC ANALYSTS. 417 are nearly the breadth of the gutter of the trough, so that they may be moved to and fro in it. dd are screens, to confine the heat and promote the draught. The combustion tube, cc, lies in a small gutter of sheet iron, upon a layer of calcined magnesia. Fig. 105. B is a gasometer with oxygen ( 66, 4) ; the cock e is connected by a brass tube with the bulb apparatus f, which contains concentrated sul- phuric acid. The handle of the cock is moved by means of a long lever, which greatly facilitates the opening and shutting. The brass tube is laterally connected, by means of a tube of vulcanized india- rubber, with a gasometer containing atmospheric air ; this part of the apparatus is omitted in the engraving. The tube g contains solid hydrate of potassa ; two or three tubes of the same description answer the pur- pose better than a single tube, cc represents the combustion tube, which is about 60 centimetres long, and open at both ends. This is connected, by means of perforated corks, at the posterior end with the potassa tube, at the anterior end with the chloride of calcium tube h : i is a potassa- apparatus ; k contains solid hydrate of potassa. The ignition of the oxide of copper is effected in the tiabe. To accomplish this, a tolerably dense stopper of copper turnings is inserted into the anterior end, the tube then filled to two-thirds of its length with oxide of copper ; the posterior orifice is then joined to g and^ as shown in the drawing, and the tube heated to gentle redness in its whole length, whilst a slow current of atmospheric air is conducted through it. After complete ignition has been effected, the spirit of wine is extinguished, the anterior end of the combustion-tube, which has up to this time remained open, connected with a small chloride of calcium tube, and the ignited oxide allowed to cool in a slow stream of atmospheric air. When the tube is cold, it is opened at the posterior end, the substance introduced into it with the aid of a long tube (com- pare 176), and quickly mixed with the oxide by means of an iron wire with twisted end (see Fig. 104) ; the after part of the tube is filled, to within about 12 centimetres, with ignited oxide of copper, cooled in the tube or flask shown in Fig. 101 ; a few gentle taps on the table will suffice to shake the contents down a little, leaving a clear passage above. The posterior end of the tube is then again connected with g, and the chloride of calcium tube, affixed to 6 during the cooling of the combuK- 418 ORGANIC ANALYSIS. [ 179. tion tube, exchanged for the one marked h*, which is accurately weighed first, and to which the weighed apparatus marked i and k are also joined. The cock, e, of the oxygen gasometer is now opened a little, so that the gas may pass in a very slow current through the apparatus ; the cock is then suddenly turned off, and the level of the fluid in the two bulb apparatus watched some time ; if no change takes place in it, this is a proof that all the joinings fit air-tight. After this, the anterior portion of the tube is heated to redness, as far as the layer of pure oxide of copper extends ; the same is then done with the farther part also, as far as the layer of pure oxide of copper extends, the corks at both ends of the tube being protected by screens, as well as also the part containing the mixture. A very slow current of oxygen gas is transmitted all the time through the apparatus. Fig. 106. The part of the tube containing the mixture is then also heated, pro- ceeding slowly from the anterior to the posterior part. The stream of oxygen gas is gradually increased, but never to an extent to allow the oxygen to escape through the potassa-apparatus, i. When the tube in its whole length is at a red heat, and the evolution of gas has ceased, the cock is opened a little wider, and the transmission of oxygen continued, until at last, when the reduced oxide of copper is completely re- oxidized, the gas begins to escape unabsorbed through the potassa-ap- paratus. The cock of the oxygen gasometer is now shut, whilst that of the air gasometer is opened a little ; the ignited charcoal is removed as far as practicable, and the combustion-tube, 36 ORGANIC ANALYSIS. [ 186. the level indicated in the drawing, either by dipping the point into the acid, and applying suction to d, or by means of a pipette. Fig. 123. 6. A soft, well-perforated CORK, which fits the combustion tube air- tight, and in which the tube d of the bulb apparatus fits closely. 7. A SUCTION TUBE filled with hydrate of potassa, and closed at the anterior end with a perforated cork, through which the point of the bulb apparatus passes. The reagents, &c., required for the ulterior treatment of the fluid obtained in the process of combustion, are omitted here, as it is not necessary to have them ready at the beginning of the operation. bb. THE PROCESS. The combustion tube is half-filled with soda-lime, which is then gra- dually transferred to the perfectly dry, and, if the nature of the substance permits, still warm mortar, where it is most intimately mixed with the weighed substance (compare 175), forcible pressure being carefully avoided ; a layer of soda-lime, occupying about 3 centimetres, is now introduced into the posterior part of the combustion tube, and the mix- ture filled-in after ; the latter, which will occupy about 20 centimetres of the length of the tube, is followed by a layer of about 5 centimetres of soda-lime, which has been used to rinse the mortar, and this again by a layer of about 10 or 12 centimetres of pure soda-lime, leaving thus about 4 centimetres of the tube clear. The tube is then closed with a plug of loose asbestos, and a free passage for the evolved gases formed by a few gentle taps ; it is then connected with the bulb apparatus by means of the perforated cork, and finally placed in the combustion furnace (see Fig. 123). To ascertain whether the apparatus closes air-tight, some air is expelled by holding a piece of red-hot charcoal to the bulb a, and the apparatus observed, to see whether the liquid will, upon cooling, permanently assume a higher position in a than in the other limb. The tube is then gradually surrounded with ignited charcoal, commencing at the anterior part, and progressing slowly towards the beak the operation being conducted exactly as in an ordinary combustion ( 175). Care must be taken to keep the anterior part of the tube tolerably hot throughout the process, since this will almost entirely prevent the formation of liquid carbides of hydro- gen, the presence of which in the hydrochloric acid would be inconvenient. The asbestos should be kept sufficiently hot to guard against its retaining water, and with this, ammonia. The combustion should be conducted so as to maintain a steady and uninterrupted evolution of gas ; there is no fear of any ammonia escaping unabsorbecl, even if the evolution is rather brisk ; whilst the analysis runs some risk from the receding of the hydrochloric acid, which inevitably takes place the very moment the 186.] ORGANIC ANALYSIS. 437 evolution of gas ceases, and this, in some instances, with such impetuosity as to force the acid into the combustion tube, which of course spoils the whole analysis. When operating upon compounds abounding in nitro- gen, even the greatest care in conducting the process will prove unavail- ing against the powerful affinity of the hydrochloric acid for the amnio- niacal gas in the tube. This may be readily prevented, however, by mixing with the substance an equal quantity of sugar, which will give rise to the evolution of more permanent gases diluting the ammonia. When the tube is ignited in its whole length, and the evolution of gas has totally ceased,* the point of the combustion tube is broken off, and a certain volume of air (three or four times the capacity of the tube) is sucked through the apparatus, to force the last traces of ammonia into the hydrochloric acid ; to guard against the inhalation of acid fumes, the s action tube is filled wi-th hydrate of potassa, or a small aspirator is used. Liquid nitrogenous compounds are weighed in small sealed glass bulbs, and the process is conducted as directed 181 (determination of carbon), with this difference, that soda-lime is substituted for oxide of copper. It is advisable to employ tubes of greater length for the combustion of liquids than are required for solid nitrogenous bodies. The best method of conducting the operation, is to heat first about one-third of the tube at the anterior end, and then to force the liquid from the bulbs into the tube by heating the hinder end of the latter; the expelled liquid will thus become diffused in the central part of the tube, without being decom- posed. By a progressive application of heat, proceeding slowly from the anterior to the posterior end, a steady and unifoi'in evolution of gas may be easily maintained. When the combustion is terminated, the bulb apparatus is emptied, through the opening at the point, into a small porcelain dish, and rinsed with water until the rinsings cease to manifest acid reaction. If liquid carbides of hydrogen have been formed, the fluid is passed through a moistened filter to separate them. Solution of pure bichloride of plati- numt in excess, is added to the filtrate, and the mixture evaporated to dryness on a water-bath ; the residue is treated with a mixture of 2 volumes of strong alcohol and 1 volume of ether. If the fluid acquires a bright yellow color, this may be taken as a proof that the quantity of bichloride of platinum added was sufficient for the intended purpose ; if not, a fresh portion of the substance (best in alcoholic solution) must be added. The residuary double salt of bichloride of platinum and chloride of ammonium is finally collected upon a weighed filter, which has been dried at 212 F., washed with the above-mentioned mixture of alcohol and ether, dried, and weighed (compare 99, 2). The dried filter is * This is indicated by the white color which the mixture re-assumes when the carbon deposited ou the surface is completely oxidized. f* If the bichloride of platinum contains an admixture of chloride of potassium or chloride of ammonium, an excess of nitrogen is the result ; if it contains an admixture of nitric acid, this will, during the evaporation, cause the formation of chlorine and the consequent destruction of a portion of the ammonia, and accordingly too little nitrogen will be obtained. It is therefore always necessary to ascertain the purity of the bi- chloride of platinum. As the double salts of platinum with some of the volatile bases produced in the decomposition of many nitrogenous organic substances (see above), are more readily soluble in alcohol than ainmonio-bichloride of platinum, ether mixed only with a few- drops of alcohol is used as washing fluid, instead of the mixture of alcohol and ether, if there is reason to suspect that such double salts of platinum are present (A . W, Hofmann). 438 ORGANIC ANALYSIS. [ 187, 188, weighed best between two close-fitting watch-glasses held together by a clasp. The bichloride of platinum and chloride of ammonium so obtained is not invariably of a pure bright yellow color, but sometimes of a darker or brownish yellow. This is the case more especially with difficultly combustible substances abounding in carbon, as it is less easy in such cases to avoid the formation of fluid carbides of hydrogen, which blacken the hydrochloric acid in the process of evaporation. Direct experiments have proved, however, that this coloration does not perceptibly impair the accuracy of the results. The purity of the bichloride of platinum and chloride of ammonium may be ascertained by reducing it to metallic platinum, according to the directions given in 99, 2. The results are very accurate ; usually somewhat too low rather than too high (about O'l to 0'2 per cent.), which is owing to traces of chlo- ride of ammonium escaping condensation in the absorption apparatus, and being carried off with the permanent gases, as is observed in every analysis of the kind. If, as is sometimes the case, the results are too high, this is principally owing to the impurity of the bichloride of platinum. y. Peligofs Modification of Varrentrapp and Wills Metliod. 187. The essential part of this modification consists in this, that the ammonia generated in the process of combustion with soda-lime, instead of being conducted into hydrochloric acid, is received in a measured quantity of sulphuric acid or oxalic acid of known strength ; the amount of free acid remaining being then determined by neutralizing with a solution of soda of known strength, and calculating from the difference the amount of acid saturated by the ammonia, and accordingly also the quantity of the latter (compare 99, 3). The most convenient way is to use the standard oxalic or standard sulphuric acid, of 215. 10 c.c. of this, containing 0'63 of crystallized oxalic acid or 0*40 of hydrated sulphuric acid, and corresponding ac- cordingly to 0'17 of ammonia, or 0*14 of nitrogen, will generally suffice for the analysis of 0'5 grm. of a substance containing 10 20 per cent, of nitrogen. The apparatus is the same as in /3 (Fig. 123). The acid is accordingly measured into a beaker ; the point of the bulb apparatus is then im- mersed in the acid, and as much as possible of the latter sucked into the bulb ; the acid adhering to the point is rinsed off. When the combus- tion is completed, the bulb apparatus is emptied into the same beaker and properly rinsed ; the fluid is then neutralized. The solution of soda must be perfectly free from carbonic acid. I prefer diluting it, so that" about 3 c.c. of it saturate 1 c.c. of the acid. This method is particiilarly well suited for technical and agriculturo- chemical investigations. With accurate measuring vessels, properly pre- pared standard fluids, and skilful manipulation, it gives results hardly less accurate than the method described in 186. C. ANALYSIS OF ORGANIC COMPOUNDS CONTAINING SULPHUR 188. The usual method of determining the carbon in organic bodies viz., 188.] ORGANIC ANALYSIS. 439 by combustion with oxide of copper or chromate of lead would give re- sults too high in the analysis of compounds containing sulphur ; since more especially if oxide of copper is used as oxidizing agent a portion, of the sulphur would be converted in the process into sulphurous acid, which would be absorbed with the carbonic acid in the potassa -apparatus. To remedy this defect, a tube 10 20 centimetres long, filled with per- fectly dry bin oxide of lead, is placed between the chloride of calcium tube and the potassa-apparatus. The binoxide of lead completely absorbs the sulphurous acid, forming sulphate of lead (Pb O 2 + S O 2 = PbO, S ) ; and thus the carbonic acid alone finds its way to the potassa- apparatus. No sulphurous acid remains in the chloride of calcium tube, if the latter is left undisturbed until the water has combined with the chloride of calcium to crystallized chloride of calcium. It is advisable after this to draw some dried air through the tube. The presence of sulphur demands no modification in the processes described 185, 186, and 187, for the determination of nitrogen. As regards the quantita- tive estimation of the sulphur in organic compounds, that element is invariably weighed in the form of sulphate of baryta, into which it may be converted either in the dry or in the moist way. In substances con- taining oxygen in presence of sulphur, the oxygen is estimated from the loss. a. Methods in tJie Dry Way. 1. Method suitable, more particularly, to determine the Sulphur in non- volatile substances poor in Sulphur, e.g., in the so-called Protein Com" pounds (Liebig). Put some lumps of hydrate of potaasa, free from sulphuric acid, ( 66, 8, c), into a capacious silver dish, add -|- of pure nitrate of potassa, and fuse the mixture, with addition of a few drops of water. When the mass is cold, add to it a weighed quantity of the finely pulverized sub- stance, fuse over the lamp, stir with a silver spatula, and increase the heat, continuing the operation until the white color of the mass shows that the carbon separated at first has been completely consumed. Should this occupy too much time, you may accelerate it by the addition of nitrate of potassa in small portions. Let the mass cool, then dissolve in water, supersaturate the solution with hydrochloric acid in a capacious beaker covered with a glass dish, and precipitate with chloride of barium. Wash the precipitate well with boiling water, first by decantation, then on the filter. Dry and ignite. Treat the ignited sulphate of baryta as directed 132, I., 1, for very accurate analyses ; if this latter operation is omitted, the result is almost always too high. 2. MetJwd adapted more particularly for the Analysis of non-volatile or diffi&dtly volatile substances containing more tlutn 5 per cent, of Sul- phur (Kolbe,, " Supplemente zum Handwb'rterbuch," p. 205). Introduce into the posterior part of a straight combustion tube,* 40 45 centimetres long, a layer, 7 8 centimetres long, of an intimate mixture of 8 parts of pure anhydrous carbonate of soda, and 1 part of pure chlorate of potassa ; after this introduce the weighed substance to be analysed, then another layer, 7 or 8 centimetres long, of the same mixture ; mix the organic compound intimately with the carbonate of soda and chlorate of potassa, by means of the mixing wire (Fig. 104 * Sealed and rounded at the end like a test tube. 440 ORGANIC ANALYSIS. [ 188. 176), to ensure its equal distribution through the entire mass ; fill up the still vacant part of the tube with anhydrous carbonate of soda or potassa mixed with a little chlorate of potassa. Clear a uncle passage from end to end by a few gentle taps, place the tube in a combustion furnace, heat the anterior part to redness, and then, progressing slowly towards the posterior part, proceed to surround with red-hot charcoal the part occupied by the mixture with the organic compound. In the analysis of substances abounding in carbon, it is advisable to introduce into the posterior part of the tube a few lumps of pure chlorate of potassa, to ensure complete combustion of the carbon, and perfect con- version into sulphates of the compounds of potassa with the lower oxides of sulphur that may have formed. The sulphuric acid in the contents of the tube is determined as in 1. 3. Method adapted for the Analysis both of non-volatile and volatile Substances, but more especially the latter (Debus, " Annal. d. Chem. und Pharm.," 76,90.) Dissolve 1 equivalent (149 parts) of bichromate of potassa purified by recrystallization, and 2 equivalents of carbonate of soda (106 parts), iu water, evaporate the solution to dryness, reduce the lemon-colored saline mass (KO, CrO g + Na O, CrO s + NaO, CO 2 ) to powder, heat to intense redness in a hessian crucible, and transfer still hot to a filling tube* (Fig. 101, 176). When the powder is cold, introduce a layer of it, 7 10 centimetres long, into a common combustion tube ; then intro- duce the substance, and after this another layer, 7 10 centimetres long, of the powder. Mix intimately by means of the mixing wire, then fill the still unoccupied part of the tube with the carbonate of soda and chromate of potassa mixture, and apply heat as in an ordinary ultimate analysis. When the entire mass is heated to redness, conduct a slow stream of dry oxygen gas over it for ^ 1 hour. W"hen cold, brush the ash off the tube, cut the latter into several pieces over a sheet of paper, transfer the pieces to a beaker, and pour over them a sufficient quantity of water to dissolve the saline mass. Add hydrochloric acid in tolerable excess, then some alcohol, and apply a gentle heat until the solution shows a beautiful green color ; filter the fluid from the sesquioxide of chromium produced by the combustion (this contains sulphuric acid); wash, first with water containing hydrochloric acid, then with alcohol, dry, and transfer the dry sesquioxide of chromium to a platinum cru- cible ; add the filter ash, mix with 1 part of chlorate and 2 parts of carbonate of potassa (or soda), and ignite until the sesquioxide of chro- mium is completely converted into chromate of potassa (or soda). Dis- solve the fused mass in dilute hydrochloric acid, and reduce by heating with alcohol ; add the solution to the fluid filtered from the sesquioxide of chromium, heat the mixture to boiling, and precipitate the sulphuric acid with chloride of barium. Debus obtained by this method very satisfactory results (99-76 and 99-50 instead of 100 of sulphur) in the experimental analysis of substances of known composition ; thus he obtained 30*2 of sulphur in the Xanthogenamide, instead of 304, Way. According to Beudant, Daguin and Rivot ("Compt. rend.," 1853, 835, "Journ. f. prakt. Chem.," 61, 135), the sulphur in organic com- pounds may be readily determined by heating with pure solution of potassa, adding 2 volumes of water and conducting chlorine into the fluid. When the oxidation is effected, the acidified solution is freed from the excess of chlorine by application of heat, then filtered, and the filtrate precipitated with chloride of barium. Mr. C. J. Merz, of my laboratory, has employed both this method and Liebig's (a, 1) in the analysis of fine horn shavings, with very satisfactory results. He ob- tained, in two experiments by Liebig's method, 3-37 and 3'345 in 100 parts of horn dried at 2 1 '2 F. ; in two other experiments by Beudant, Daguin and Rivofs method, 3'31 and 3'33 per cent. %* Substances leaving ash on incineration, and which may therefoi-e be presumed to contain sulphates, are boiled with hydrochloric acid ; the solution obtained is filtered, and the filtrate tested with chloride of barium. If a precipitate of sulphate of baryta forms, the sulphur contained in it is deducted from the quantity found by one of the methods described above ; the difference gives the quantity of the sulphur which the ana- lysed substance contains in organic combination. 442 ORGANIC ANALYSIS. [ 189, 190. D. DETERMINATION OF PHOSPHORUS IN ORGANIC COMPOUNDS. 189. Mulder, who lias occupied himself more than any other chemist with the determination of phosphorus in organic substances, recommends the following method : Dissolve a weighed portion of the substance by boiling with hydro- chloric acid ; filter, if necessary, and determine the phosphoric acid which the fluid may contain, by Berthier's method ( 134, I., d). Boil another weighed portion of the substance with nitric acid, and treat the fluid in the same way as the hydrochloric acid solution. If you find in both the same per-centage amount of phosphoi'ic acid, the analysed substance contains the phosphorus only in the form of phosphoric acid ; but if you obtain a larger proportion of acid in the second experiment than in the first, the difference indicates the quantity of phosphoric acid formed by the action of the nitric acid upon phosphorus contained in the analysed compound in the non-oxidized state. Thus, for instance, Mulder found in caseine in both experiments 3 '5 per cent, of phosphoric acid, whilst in the analysis of albumen the hydrochloric acid solution gave O35 per cent., the nitric acid solution 0*78 per cent, of that acid. The phosphorus cannot be determined by incineration of the substance and examination of the ash. Vitellin, which, when treated with nitric acid, gives 3 per cent, of phosphoric acid, yields barely 0*3 per cent, of ash (Baumhauer). The methods described in 188, a, 1, 2, 4, and b, may also be em- ployed to determine the total quantity of phosphorus in organic com- pounds. E. ANALYSIS OF ORGANIC COMPOUNDS CONTAINING CHLORINE (BROMINE OR IODINE). 190. The combustion of organic compounds containing chlorine with oxide of copper gives rise to the formation of subchloride of copper, which, were the process conducted in the usual manner, would con- dense in the chloride of calcium tube, and would thus vitiate the determination of the hydrogen. This and every other defect may be readily remedied, however, by substituting chromate of lead for oxide of copper, and conducting the process exactly as directed 177. The chlorine is, in that case, converted into chloride of lead, and retained in that form in the combustion tube. If the combustion is effected with oxide of copper in a current of oxygen gas, the subchloride of copper formed is decomposed by the oxygen into oxide of copper and free chlorine, which latter element is retained partly in the chloride of calcium tube, partly in the potassa- apparatus. To remedy this defect, Stcideler (" Anna!, d. Chem. u. Pharm.," 69, 335) proposes to retain the chlorine in the tube, by filling the anterior part of the latter with clean copper turnings, to be kept red hot during the process of combustion, and arresting the current of oxygen the moment the copper turnings begin to oxidize. According to A. Volcker ("Chem. Gaz.," 1849, 245), the evolution of chlorine may be avoided, by adding to the oxide of copper of oxide of lead. 191.] ORGANIC ANALYSIS, 443 As regards the determination of the chlorine in organic compounds containing that element, this is invariably effected by igniting the sub- stance with alkalies or alkaline earths, by which process all the chlorine is obtained as chloride. Lime free from chlorine (which is easily obtained by the calcination of marble) is usually employed as a decomposing agent ; the lime used must always be carefully tested, to make quite sure that it contains no chlorine. Introduce into a combustion tube, about 40 centimetres long, the posterior end of which is sealed and rounded like a test tube, a layer of lime, 6 centimetres long, then the substance, after this another layer of lime, 6 centimetres long, and mix intimately with the wire ; fill the tube almost to the mouth with lime, clear a free passage for the evolved gases by a few gentle taps, and apply heat in the usual way. If you have to operate upon volatile fluids, introduce them into the tube in small glass bulbs. When the decomposition is terminated, dissolve in dilute nitric acid, and precipitate with solution of nitrate of silver ( 141). Kolbe recommends the following process to obtain the contents of the combus- tion tube : when the decomposition is completed, remove the charcoal, insert a cork into the open end of the tube, brush away every particle of ash, and immerse the tube still hot, with the sealed end downwards, into a beaker filled two-thirds with distilled water ; the tube breaks into many pieces, and the contents are then more readily acted upon. As in this method the ignition of compounds abounding in nitrogen may be attended with formation of cyanide of calcium or cyanide of sodium, the separation of the chloride and cyanide of silver, if required, is to be effected by the process given in 169, 6, b (Neubauer and Kerner, " Annal. d. Chem. u. Pharm.," 101, 324, 344). In the analysis of acid organic compounds containing chlorine (e.g., chlorospiroylic acid), the chlorine may often be determined in a simpler manner, viz., by dissolving the substance under examination in an excess of dilute solution of potassa, evaporating to dryness, and igniting the residue, by which means the whole of the chlorine present is converted into a soluble chloride (Lowig). Organic compounds containing bromine or iodine are analysed in tha same manner as those containing chlorine. F. ANALYSIS OF ORGANIC COMPOUNDS CONTAINING INORGANIC BODIES. 191. In the analysis of organic compounds containing inorganic bodies, it is, of course, necessary first to ascertain the weight of the latter before proceeding to the determination of the carbon, &c., as otherwise the amount of the organic substance, whose constituents have furnished the carbonic acid, water, &c., not being known, it would be impossible to estimate the quantity of oxygen from the loss. If the organic bodies in question are salts or similar compounds, their bases are determined by the methods given in the Fourth Section ; but in cases where the inorganic admixtures are of a nature to be regarded more or less as impurities (e.g., the ash in wheaten flour), they may usually be determined with sufficient accuracy by the combustion of a weighed 44-4) ORGANIC ANALYSIS. [ 192. portion of the substance in an obliquely placed platinum crucible, or in a platinum dish, with use of a cylinder to promote the draught (see " Analysis of Ashes). In the analysis of substances containing fusible salts, even long continued ignition will often fail to effect complete com- bustion, as the carbon is protected by the fused salt from the action of the oxygen. In such cases, the best way to effect the purpose is to car- bonize the substance, treat the mass with water, and incinerate the un- dissolved residue ; the aqueous solution is, of course, likewise evaporated to dryness, and the weight of the residue added to that of the ash (com- pare Special Part, " Analysis of Ashes"). If organic compounds whose ash contains potassa, soda, baryta, lime, or strontia, are burnt with oxide of copper, part of the carbonic acid evolved remains combined with the alkalies or earths. As, in many cases, the amount of carbonic acid thus retained is not constant, and the results are, moreover, more accurate if the whole amount of the carbon is expelled and determined as carbonic acid, the oxide of copper is mixed with substances which will effect the decomposition of the carbonates at a high temperature, e.g. teroxide of antimony, phosphate of copper, boracic acid (Fremy), &c.; or the combustion is effected with chromate of lead, with addition of y^th of bichromate of potassa, according to the directions given in 177. The latter method deserves the preference. Accurate experiments have shown that in a combustion effected with chromate of lead and bichromate of potassa, not a trace of carbonic acid remains with the bases. If the organic substance containing such fixed constituents, is weighed in a small porcelain or platinum boat, the ash, carbon, and hydrogen may be determined in one and the same portion. The amount of car- bonic acid contained in the ash is added to that found by the process of combustion ; if the carbonic acid in the ash cannot be calculated, as in the case of carbonates of the alkalies, it may be determined by means of fused borax ( 139, U.,d). III. DETERMINATION OF THE EQUIVALENT OF ORGANIC COMPOUNDS. The methods of determining the equivalent of organic compounds differ essentially according to the nature and properties of the various compounds. There are three general methods in use for this purpose, 1. We take a Substance of known Equivalent and determine the exact quantity of it which forms a Definite and well characterized Compound with the Body whose Equivalent we wish to Determine. This method is pursued in determining the equivalent of the organic acids and organic bases, and of many indifferent bodies possessed of the property of combining with bases. We occupy ourselves here simply with the analytical process; the mode of calculating the equivalent from the results obtained will be found in the chapter on the Calculation of Analyses. a. The equivalent of organic acids is, in most cases, determined from the silver salt of the acid, because the analysis of this is very simple, and there is almost always the positive certainty that the analysed salt is not a basic or hydrated compound. Other salts also are, however, frequently used for the same purpose, particularly the lead, baryta, and 193.] ORGANIC ANALYSIS. 445 lime salts of organic acids. In the analysis of the lead salts of organic acids, especial care must be taken not to mistake basic for neutral, nor in. the analysis of the baryta and lime salts, hydrated for anhydrous salts. For the manner in which the quantitative determination of the bases in question is effected, I refer to Section IV. b. The equivalent of organic bases forming crystallizable salts with sulphuric acid, hydrochloric acid, or any other easily determined acid, is best ascertained by estimating, by the usual methods, the proportion of the acid contained in a weighed amount of the salt. If the salts do not crystallize, a known quantity of the dried alkaloid is introduced into a drying tube (Fig. 124), which is then accurately weighed with its con- tents ; a slow current of dry hydrochloric acid gas is transmitted through the apparatus for some time ; the tube ultimately heated to 212 F. (see 28, Fig. 29), and a stream of atmo- spheric air transmitted through it; the quantity of the hydrochloric acid absorbed is found Fig. 124. from the increase in the weight of the tube. The accuracy of the results may be controlled by dissolving the hydro- chlorate in water, and precipitating the chlorine from the solution by nitrate of silver. The equivalent of the alkaloids may be determined also from the insoluble double salts produced by precipitating the solu- tion of their hydrochlorates with bichloride of platinum ; the double chlorides thus produced are cautiously ignited, 124, and the residuary- platinum accurately weighed. c. In the case of indifferent bodies, there is usually no other choice left than to determine the equivalent from the lead compound ; since these substances either altogether refuse to enter into combination with other bases besides lead, or form with them compounds only which cannot be obtained in a state of purity. Although the determination of the equivalent of an indifferent body from the compound which the latter forms with lead, is liable to leave the matter in doubt, as the oxide of lead will often combine with such substances in varying proportions, yet the analysis of such compounds is always interesting in this that we learn by it whether the organic body combines with the lead without alteration, or gives up water upon entering into combination with that metal. Organic substances will also occasionally form with water solid and crystallizable compounds, by the analysis of which the equivalent 01 the organic body may be determined. 193. 2. The Specific Gravity of tJte Vapor of tlie Compound is determined (Dumas). The following are the outlines of Dumas' method, which I shall immediately after proceed to describe more in detail. A light glass globe, filled with dry air, and the exact capacity of which is afterwards ascertained, is accurately weighed ; the weight of the air in the globe is calculated at the temperature and atmospheric pressure observed during the process of weighing, and the result subtracted from the first weight: the difference expresses the weight of the exhausted vessel. A more than sufficient quantity of the substance, the density of the vapor of 446 .ORGANIC ANALYSIS. [ 193. which it is intended to determine, is then introduced into the globe, and exposed to a uniform temperature exceeding the boiling point of the substance, until the latter is completely converted into vapor, and the excess expelled together with the atmospheric air originally contained in the globe ; the vessel is then sealed air-tight, and accurately weighed. The difference between the weight found and that of the exhausted globe, .expresses the exact weight of a volume of the vapor corresponding to the capacity of the globe ; supplying thus the necessary data for calculating the density of the vapor. It is hardly necessary to remark that the volume of the vapor must first be calculated at the usual height of the barometer, and 32 F. of the thermometer, and consequently that the state of the barometer and ther- mometer must be correctly noted both during the first weighing and at the time of sealing the glass globe. This method is of course applicable only to substances which volatilize without suffering decomposition. To obtain accurate results, it is indis- pensable that the examined substance be perfectly pure. I will now proceed to describe the analytical process; for the manner of correcting and calculating the results, arid inferring the composition of the analysed bodies from them, I refer to the chapter on the "Cal- culation of Analyses " ( 204). a. Apparatus and other Requisites. 1. THE SUBSTANCE. From 6 to 8 grammes are required. The boil- ing point of the substance must be pretty accurately known. 2. A LIGHT GLASS GLOBE WITH DRAWN-OUT NECK. A light globe of pure glass is selected, free from flaws and holding from 250 to 500 cubic centimetres ; it is carefully rinsed with water, and then thoroughly dried. After this, it is completely exhausted, dry air readmitted into it, and the same operation repeated several times (the apparatus illustrated in Fig. 97, 175, is used for this purpose). The neck of the globe is then softened near the bulb, and drawn out in the shape represented in Fig. 125. The extreme point is cut off, and the edges slightly rounded over the the spirit-lamp ; this point having to be sealed air-tight with the greatest despatch, at a subsequent stage of the process, it is advisable to ascertain, in the first place, whether the glass of the globe is readily fusible or not j this may be done by trying to seal the point of the original neck of the balloon, previous to drawing it out ; should this present any difficulty, the globe is totally unfit for the intended purpose. ^^^^^^^ 3. A SMALL IRON OR COPPER VESSEL for the reception Fig. 125. of the fluid in which the globe is to be heated (see Fig. 126). The fluid which is to serve as bath must admit of being heated to at least 54 or 72 F. beyond the boiling point of the substance under examination. Oil will answer the purpose in all cases where a temperature higher than that of boiling water is re- quired ; however, a chloride of calcium bath if its temperature, which in a perfectly saturated bath may be raised to 356 F., is sufficiently high for the purpose is more convenient than an oil-bath, as the globe may be more easily cleaned. 4. AN APPARATUS TO KEEP THE GLOBE IN POSITION. This may be 193:] ORGANIC ANALYSIS. 447 readily made with a handle and some iron wire. During the operation, it is attached to a retort stand (see Fig. 126). 5. A quantity of MERCURY more than sufficient to fill the globe. 6. An accurately GRADUATED TUBE of about 100 cubic centimetres capacity. 7. SPIRIT-LAMP and BLOWPIPE. 8. A correct BAROMETER. 9. A correct THERMOMETER, capable of indicating the highest degree of heat the case under examination may require. b. The Process. a. Weigh the globe on the balance, placing a thermometer inside the case. Leave the globe for 1 minutes on the scale, to ascertain whether its weight remains constant. If so, the weight is noted, together with the height of the barometer, and the temperature indicated by the ther- mometer inside the case. /3. Introduce about 8 grammes of the fluid or, by the application of a gentle heat, liquefied substance into a glass ; heat the globe gently, and dip the pointed end deep into the liquid. If the substance under ex- amination has a high fusing point, the neck and point of the globe like- wise require heating, to guard against the fluid solidifying in the neck. As soon as the globe cools which, in the case of very volatile sub- stances, is accelerated by dropping ether upon it the fluid enters and spreads in it. Do not introduce more than 5 7 grammes. y. Heat the contents of the vessel (3) to 104 122 F., and immerse the globe by means of the apparatus (4), and also a thermometer, in the bath as shown in Fig. 126. Raise the temperature of the bath to the required point.* As soon as the temperature in the globe is somewhat higher than the boiling point of the substance, the vapor of the latter rushes out through the orifice of the neck ; the force of the current increases at first with the temperature of the bath, but diminishes afterwards by de- grees, and ceases finally alto- gether (after about 15 minutes). Should any of the vapor have condensed into drops in the point of the neck projecting above the surface, these may be at once re- converted into vapor, by moving a piece of red-hot charcoal to and fro round it. The moment that a perfect equilibrium is fully es- Fi g< 126. tablished at the desired tempe- rature, seal the point of the globe hermetically, by means of a spirit- lamp and blowpipe, and note immediately after the height of the ther- mometer. To ascertain whether or not the point is hermetically sealed, you need simply direct a current of air through the blowpipe upon the * If the globe is immersed in a chloride of calcium or oil-bath, you must endeavor to maintain a uniform temperature towards the end of the process, which may be easily effected by properly regulating the heat. 448 ORGANIC ANALYSIS. [ 194. projecting point of the neck : if the tube is closed hermetically, a small portion of the vapor condenses, forming a column of fluid, which is re- tained in the end of the tube by capillary attraction ; this is not observed if the tube is not hermetically sealed. The height of the barometer also is noted again, if it has changed since the first obser- vation. 2. Remove the sealed globe from the bath, allow to cool, wash most carefully, wipe perfectly dry, and weigh again in the same manner as before. c. Immerse the pointed end of the globe in its entire length in mer- cury, scratch a mark with a file near the end, and break off the point ; whereupon the mercury will immediately rush into the globe, a vacuum having been created in it by the condensation of the vapor. In this operation, place the glass globe in the hollow of your hand, and rest the latter upon the edge of the mercurial trough. If the globe, at the moment of sealing, was perfectly free from air, it will fill completely with mercury ; otherwise an air bubble will remain in it. In either case transfer the mercury from the globe to the graduated tube (6), and measure accurately ; if there was air in the globe at the moment of sealing it, fill it now with water, and measure also the volume of the latter liquid : the difference between the volume of the mercury and that of the water shows the volume of the air which had remained in the globe. This method, if properly executed, gives nearly accurate results ; for the manner of calculating the latter, 1 refer to the chapter on the " Cal- culation of Analyses" ( 204). 194. 3. A great many indifferent organic bodies absolutely refuse to com- bine with bases or acids, as, e.g., salicine ; or form with them only com- pounds, from which the equivalent of the organic body cannot well be determined, as e.g., phloridzin. The equivalent of such substance is determined by producing by the action of acids, bases, halogens, tic., upon the body under examination, new compounds of known or ascer- taiuable equivalents. Or, lastly, the equivalent is inferred from the manner in which the compound in question has been formed. In cases of this description, that equivalent is assumed to be the correct one which permits the most simple explanation of the processes of formation and decomposition. This latter mode of determining the equivalent of substances is inti- mately connected with the higher branches of organic chemistry, and cannot be considered in detail here, as it is impossible to give universally applicable methods. Supplement. " ON THE USE OF GAS AS FUEL IN ORGANIC ANALYSIS."* Dr. Hqfmann has lately succeeded in providing our laboratories with a combustion furnace which has met with the general approval of * By A. W. ffofmann. Extracted from the "Quarterly Journal of the Chemical Society," TO!, yi. p. 209. 194.] ORGANIC ANALYSIS. 449 chemists, and has been rapidly introduced into most of the English labo- ratories where gas furnishes the fuel for chemical operations. Its superiority over any of the proposed combustion furnaces is acknowledged by all who have recently adopted it. The construction of he apparatus being obvious from the accompanying wood-cuts, a few explana- tory remarks will be sufficient. Into a brass tube, of from 3 feet to 3 feet 8 inches length, and 1 inch diameter (shown in section in Fig. 128), which com- municates at both ends with the gas-main of the laboratory, there are screwed from twenty-four to thirty-four tubes. These tubes, ^ inch thick and 7 inches high, are provided with stopcocks, and carry brackets, of 4^ inches length and |-inoh dia- meter, for the reception of five ordinary bat's-wing burners (each consuming from 3 to 4 cubic feet of gas per hour for a full luminous effect) upon which a corresponding number of clay-burners are fixed. The high clay burners, represented in Fig. 127, are 3 inches high, of |-inch exterior, and f-inch interior diameter. The perforations, which are of about the thickness of a pin, are made in rows ; their number varies ; those employed for Dr. Hof- mann's fumace have ten rows, each of fifteen holes. From such a clay cylinder, loosely fixed upon an ordinary bat's-wing burner, the stopcock of which has been appropriately adjusted, the gas burns with a perfectly blue flame which envelopes the cylinder, and renders it in a short time incandescent. The small burners are only 1| inches high, and have only seventy or eighty perforations. A row of these smaller burners serves as support for the combustion tube which is thus bedded in a channel of heated fire- clay. The system of brackets lying side by side acquires sufficient stability by a strong iron frame, which rests upon two firm sup- ports, of cast iron, fastened down by screws upon the foot-plate, likewise of cast iron. The iron frame has moreover a groove for the reception of moveable side plates of fire-clay. They are of the same height as 'the high burners, over which they project, however, about | inch, in consequence of their resting upon the frame ; lastly, there are covering plates, likewise of fire-clay, which are sup- ported by the side plates. Fig- 128. The whole disposition of this apparatus will be best understood by a glance at the perpective view given in Fig. 129. In the front part, contiguous to the potassa-apparatus, the side plates and the covering plates are omitted, in order to show the disposition of the burners. During the combustion, however, all the burners are in- closed, as exhibited in the posterior part of the apparatus!. II. G G Fig. 127. 450 ORGANIC ANALYSIS. [ 194. It deserves to be noticed that the efficiency of the furnace essentially depends upon the correct disposition of the gas-jets. The most appro- priate space between the several burners, according to numerous experi- ments made for the purpose, is about ^ inch. It is very important, for the attainment of a perfectly uniform temperature, that the several brackets bearing the burners should be equidistant. Their position is therefore specially secured by every bracket being fixed in an aperture formed in the iron frame, (Fig. 128). Fig. 129. The use of the furnace scarcely requires any special remark. Accord- ing to the length of the combustion tube, from 8 to 1 stopcocks (under all circumstances the largest possible number,) are opened at once at the commencement of a combustion. If care has been taken to regulate the amount of gas, either by the stopcocks in the horizontal gas-pipe, or by those in the separate supply-tubes, the lighted portion of the furnace, in 10 or 12 minutes, will be in a state of perfect incandescence, comparable only to the ignited mass of charcoal in an ordinary combustion furnace. After this it is only necessary to open the remainder of the stopcocks in appropriate succession, to insure a slow and regularly progressing combustion. The time required for the completion of an analysis varies : from 40 minutes to an hour. Only in extraordinary cases a longer time may be required. The heat obtained by this furnace is extremely uniform, and since it is conveyed to the combustion tube chiefly by radiation from the incan- descent mass of surrounding clay, every part of the tube is equally heated. It is in this respect especially that the new apparatus differs from all former contrivances of this kind. The temperature which it is capable of yielding is entirely at the command of the operator. When strained to its full power, it gives a heat equal to that of the strongest charcoal combustion furnace, at which even the most refractory Bohe- mian tubes readily fuse ; by appropriately adjusting the stopcocks, however, it is possible to maintain the furnace at any desired tempera- ture, especially since it is only necessary to look into the channel, when," with a little practice, a correct idea of the temperature is rapidly obtained from the color of the glowing cylinders. It deserves, however, to be noticed, that the apparatus furnishes rather more than less heat than is generally required ; it is preferable, therefore, under all circum- stances, to protect the combustion tube by a metallic shield : for this purpose ordinary brass-wire gauze maybe conveniently employed ; which 194.] OEGANIC ANALYSIS. 451 is more easily manipulated, and may be used longer than the thin copper or brass plate generally employed. From what has been stated it is obvious that the furnace may be used in many operations in which charcoal has hitherto been considered almost indispensable. The combustion may be made with or without oxygen, as the case may necessitate. In all other tube operations, in passing gases or vapors through red-hot tubes (preparation of propylene gas), in reducing copper turnings, tnat is _10-5 9-1833 _ 1-3162 = _ 0-10419 0-1041$ K = 20 12-63 = 7-37. The 20 grammes of the mixture consist accordingly of 12'63 Na 0, 5 3 , and 7-37 K O, S 3 . 0. Suppose we have found 3 grammes of chloride of sodium and chloride of potassium, and in these 3 grammes 1-6888 of chlorine. Equ. of Chlorine. Equ. of K Cl. Chlorine found. 35-46 : 74-57 :: 1-6888 : x x = 3-5514 If all the chlorine present were combined with potassium, the weight af the chloride would amount to 3-5514. As the chloride weighs less, chloride of sodium is present, and this in a quantity proportional to the difference, i. e., 3-5514 3 = 0-5514, which is calculated by the following proportion : The difference between the equivalent of K Cl and the equivalent of Nad (16-11) is to the equivalent of Nad (58-46), as the difference found to the chloride of sodium present ; or, expressed in numbers : 16-11 : 58-46:: 0-5514 : x o; = 2NaCl and 3 - 2 = 1 K CL From this the following short rule is derived : Multiply the quantity of chlorine in the mixture by 2'1029, deduct 462 CALCULATION OP ANALYSES. [ 200, from the product the sum of the chlorides, and multiply the difference by 0-36288 ; the product expresses the quantity of chloride of sodium contained in the mixed chloride. The following formulae will serve to find the sodium and potassium by direct calculation : Let x stand for potassium, y for sodium, S for the mixed chloride, A. for the chlorine found. [(S-A). 1-54] -A 0-63 A-[(S-A). 0-91] 0-63 ifii C1 Na 0,1= g ' b. Indirect Determination of Strontia and Lime. This may be effected by determining the sum total of the carbonates, and the carbonic acid contained in them ( 154,6). Suppose we have found 2 grammes of mixed carbonate, and in these 2 grammes 0-7386 of carbonic acid. Equ. of C 0, Eqn . of Sr 0, C 0, C 0, found. 22 : 73-67 :: 0-7386 : x x = 2-47335 If, therefore, the whole of the carbonic acid were combined with strontia, the weight of the carbonate would amount to 2-47335 grma. The deficiency, = 0-47335, is proportional to the carbonate of lime present, which is calculated as follows : The difference between the equivalent of Sr 0, C O a , and the equiva- lent of Ca 0, C O a (23-67) is to the equivalent of Ca 0, C O, (50), as the difference found to the carbonate of lime contained in the mixed salt ; or, expressed in numbers : 23-67 : 50 :: 0-47335 : x The mixture, therefore, consists of 1 gramme of carbonate of lime and 1 gramme of carbonate of strontia. From this the following short rule is derived : Multiply the carbonic acid found by 3-3487, deduct from the product the sum of the carbonates, and multiply the difference by 2-1125 ; the product expresses the quantity of the carbonate of line. c. Indirect Determination ofCJdorine and Bromine ( 169,1). Let us suppose the mixture of chloride and bromide of silver to have weighed 2 grammes, and the diminution of weight consequent upon the 201.] CALCULATION OF ANALYSES, 463 transmission of chlorine to have amounted to 1 gramme. How much chlorine is there in the mixed salt, and how much bromine ? The decrease of weight here is simply the difference between the weight of the bromide of silver originally present, and that of the chloride of silver which has replaced it ; if this is borne in mind, it is easy to understand the calculation which follows : The difference between the equivalents of bromide of silver and chlo- ride of silver is to the equivalent of bromide of silver as the ascertained decrease of weight is to x, i.e., to the bromide of silver originally present in the mixture ; or, expressed in numbers : 44-507 : 187-942 : : 0-1 : x x = 0-42227. The 2 grammes of the mixture [therefore contained 0-42227 grm. of bromide of silver, and consequently 2 - 0*42227 = 1 -57773 grm. of chlo- ride of silver. It results from this calculation, that we need simply multiply the ascertained decrease of weight by to find the amount of bromide of silver originally present in the analysed mixture. And if we know this, we also know of course the amount of the chloride of silver ; and from these data we deduce the quantities of chlorine and bromine, as directed in 2, and the proportions of these two substances contained in 100 parts by weight of the analysed compound, as directed in 1. SUPPLEMENT TO I. MEAN VALUE, DEFICIENCY, AND EXCESS IN ANALYSES. 201. If, in the analysis of a substance, one of the constituents is estimated from the loss, or, in other words, by subtracting from the original weight, of the analysed substance the ascertained united weight of the other constituents, it is evident that in the subsequent per-centage calcu- lation the sum total must invariably be 100. Every loss suffered or excess obtained in the determination of the several constituents will, of course, fall exclusively upon the one constituent which is estimated from the loss. It is evident, therefore, that quantitative estimations of this kind can afford no guarantee of correctness, unless the other constituents have been determined by good methods, and with the greatest care. The accuracy of the results will of course be the greater, the less the number of constituents determined in the direct way. If, on the other hand, every constituent of the analysed compound has been determined separately, it is obvious that, were the results absolutely accurate, the united weight of the several constituents must be exactly equal to the original weight of the analysed substance. Since, however, as we have seen in 96, certain inaccuracies attach to every analysis, without exception, the sum total of the results in the 464 CALCULATION OP ANALYSES. [ 201. per-centage calculation will sometimes exceed, and at others fall short of, 100. In all cases of this description, the only proper way is to give the results as actually found. So, for instance, Pelouze found, in his analysis of chromate of chloride of potassium, Potassium 21 '88 Chlorine 19-41 Chromic acid 58-21 99-50 Berzelius, in his analysis of sesqui oxide of uranium and potassa, Potassa 12-8 Sesquioxide of uranium 8 6 '8 99-6 Plattner, in his analysis of magnetic iron pyrites. OfFahlun. Of Brasil Iron 59-72 59-64 Sulphur 40-22 40-43 99-94 100-07 It is altogether inadmissible to distribute any chance deficiency or excess, proportionally among the several constituents of the analysed compound, as such deficiency or excess of course never arises from the several estimations in the same measure; moreover, such a way of arranging the calculation of the results deprives other chemists of the power of judging of the accuracy of the analysis. No one need be ashamed to confess having obtained somewhat too little or somewhat too much in an analysis, provided, of course, the deficiency or excess be con- fined within certain limits, which differ in different analyses, and which the experienced chemist always knows how to fix properly. In cases where an analysis has been made twice, or several times, it is usual to take the arithmetical mean as the correct result. It is obvious that an average of the kind deserves the greater confidence the less the results of the several analyses differ. The results of the several analyses must, however, also be given, or, at all events, the maximum and minimum. Since the accuracy of an analysis is not dependent upon the quantity of substance subjected to the analytical process (provided always this quantity be not altogether too small), the average of the results of several analyses is to be taken quite independently of the quantities used; in other words, you must not add together the quantities used, on the one hand, and the weights obtained in the several analyses on the other, and deduce from these data the per-centage amount ; but you must calculate the latter from the results of each analysis separately, and then take the arithmetical mean of the numbers so obtained. Suppose a substance, which we will call AB, contains fifty per cent, of A; and suppose two analyses of this substance have given the following results : $ SU2.] CALCULATION OF ANALYSES. 465 1) 2 grammes of AB have given 0-99 grm. of A. 2) 50 24-00 From analysis No. 1, it results that AB contains 49 '50 per cent, of A. No. 2, 48-00 Total .{ 97-50 Mean 48-75 It would be quite erroneous to say 2 + 50 = 52 of AB gave 0-99 + 24-00 = 24-99 of A, therefore 100 of AB. contain 48-06 of A ; for it will be readily seen that this way of calculating destroys nearly altogether the influence of the more accurate analysis of the two (1) upon the average, on account of the proportionally small amount of substance used in that analysis. II. DEDUCTION OF EMPIRICAL FORMULE. 202. If the per-centage composition of a substance is known, a so-called empirical formula may be deduced from this ; in other words, the rela- tive proportion of the several constituents may be expressed in equiva- lents in a formula which, upon recalculation in per-cents will give numbers corresponding perfectly, or nearly, with those obtained by the analysis of the substance in question. We are compelled to confine our- selves to the expression of empirical formulae, in the case of all substances of which we cannot determine the equivalent, as e.g., mannite, woody fibre, mixed substances, &c. The method of deducing empirical formulae is very simple, and will be readily understood from the following reflections : How should we proceed to find the relative number of equivalents in carbonic acid ? We should say : The equivalent of the oxygen is to the amount of oxygen in the equi- valent of carbonic acid, as 1 is to x, i.e., to the number of equivalents of oxygen contained in carbonic acid ; accordingly 8 : 16::1 : x x = 2. In the same manner we should find the number of equivalents of carbon present in carbonic acid, by the following proportion : 6 : 6 :: 1 : x (equivalent of carbon) (carbon in one equivalent of carbonic acid.) C=1. Now let us suppose we did not know the equivalent of carbonic acid, but simply its per-centage composition, viz., 27-273 of carbon. 72-7:27 of oxygen 100-000 of carbonic acid, II. H H 466 CALCULATION OP ANALYSES. [ 202. the relative proportion of the equivalents might still be ascertained, even though any other given number, say 100, be selected for the equiva- lent of carbonic acid. Let us suppose we adopt 100 as the equivalent of carbonic acid ; thus, 8 : 72-727 :: 1 : x (Equ. of 0) (Amount of oxygen in the assumed equivalent of 100) x =9-0910 and 6 : 27-273 :: 1 : x (Equ. of C) (Amount of carbon in the assumed equivalent of 100) x = 4-5455. We see here that although the numbers which express the relative pro- portion of the atoms of oxygen and carbon, have changed, yet the relative proportion remains the same ; since 4-5455 : 9-0910::! : 2. The process may accordingly be expressed in general terms as follows : Assume any number, say 100 (because this is the most convenient), as the equivalent of the compound for which you wish to establish an empirical formula, and ascertain how often the equivalent of each con- stituent severally is contained in the amount of the same constituent resulting from the analysis. When you have thus found the numbers expressing the relative proportion which the several constituents bear to each other, you have attained your purpose viz., the deduction of an empirical formula. Still, it is usual to reduce the numbers found to the simplest expression. Now let us take a somewhat complicated case, e.g., the deduction of the empirical formula for mannite. The per-centage composition of mannite is 39-56 of carbon 7-69 of hydrogen 52 -75 of oxygen 100-00 This gives the following proportions : 6 : 39-56::! : x x = 6-593 1 : 7-69 = 1 :x x = 7-690 8 : 52-75 = 1 : x x =6-593 We have now the empirical formula for mannite, viz., A glance shows that the number of the equivalents of the carbon is equal to that of the equivalents of the oxygen ; and the question is now whether the relative proportion found may not be expressed by smaller numbers. 202.] CALCULATION OF ANALYSES. 467 A simple calculation suffices to answer this question, viz., 6-593 : 7-690:: 60 : x (Any other number might be substituted for 60, as the third term ot the proportion, but 60 is the most convenient, since it is divisible with- out remainder by most of the numbers.) x=7Q We have accordingly now the simple formula, . C*o H ro 60 = C 6 H 7 O, The per-centage composition of mannite given above having been de- duced from the results of actual analyses, the correctness of the formula derived from it cannot be called in question. Now let us take the re- sults of a direct analysis of mannite. Oppermann obtained, upon the combustion of 1-593 gnn. of mannite, with oxide of copper, 2-296 grammes of carbonic acid and 1'106 grm. of water. This gives by calculation in per-ceuts. 39-31 of carbon 7 '71 of hydrogen 52-98 of oxygen 100-00 which, calculated as above, gives I 0, SiO^ Aq. Besides isomorphous substances, all bodies of analogous composition possess the faculty of replacing each other in compounds ; thus we find that KO, Na O, Ca 0, Mg O, &c., replace each other. These substances likewise must be expressed collectively in the formula. Abich found in Andesine Amount of Oxygen. Silicic acid 59-60 ..... 30-94 Alumina 24-28 . .11-22) n 7n Sesquioxide of iron 1-58 . . 0-48 } ' Lime 5-77 1-61 Magnesia 1-08 . . 0-43 , o QA Soda 6-53 . . 1-68 y ' 1-08 . 0-18 99-92 472 CALCULATION OF ANALYSES. [ 204. The ratio between 3-90 : 11-70 : 30-94 is as 1 : 3 : 7-93 ; for which we may safely substitute 1:3:8. Designating 1 equivalent of metal by R, we obtain from these numbers the formula : R O + R 2 O. + 4 Si O a = RO, Si0 2 + R 2 s , 3Si0 2 , tten : A1 2 ) ),Sio 2+F Vo 3 which may likewise be written : Ca 0,Si0 1+ 'J-O^SSiO,. Showing thus that this mineral is Leudte (K O, Si 2 4- A1 2 3 , 3 Si 2 ), iu which the greater part of the potassa is replaced by lime, soda, and magnesia, and a portion of the alumina by sesquioxide of iron. These remarks respecting the deduction of formulae for oxygen salts, apply of course equally to metallic sulphides. IV. CALCULATION OF THE DENSITY OF THE YAPORS OF VOLATILE BODIES, AND APPLICATION OF THE RESULTS, AS A MEANS OF CON- TROLLING THEIR ANALYSES, AND DETERMINING THEIR EQUIVALENTS. 204. The specific gravity of a compound gas is equal to the sum of the specific gravities of its constituents in one volume. E.g., 2 volumes of hydrogen gas and 1 volume of oxygen gas give 2 volumes of aqueous vapor. If they gave simply 1 volume of aqueous vapor, the specific gravity of the latter would be equal to the sum total of the specific gravity of the oxygen and double the specific gravity of the hydrogen viz., 2x0-0693 = 0-1386 + 1-1083 = 1-2469 But as they give 2 volumes of aqueous vapor, these 1-2469 are dis- tributed between the 2 volumes; accordingly !*_ 0-62345 It will be readily seen that the knowledge of the density of the vapor of a compound supplies an excellent means of controlling the cor- rectness of the relative proportions .of the equivalents assumed in a formula, provided the density has been determined at a temperature, at least 54-72 F., above the boiling point of the analysed substance; as it is only under these conditions that the actual and constant density of the vapor can be ascertained. 20i.] CALCULATION OF ANALYSES. 473 For instance : from the results of the ultimate analysis of camphor, has been deduced the empirical formula : C 10 H 8 0. Dumas found the density of the vapor of camphor = 5-312. Now, by what means do we find whether this formula is correct with respect to the relative proportions of the equivalents ? Specific gravity of the vapor of carbon 0-831 hydrogen gas 0-0693 oxygen gas 1-108 lOequ. 0=10 volumes =10x0-831 =-8-310 Sequ. H= 16 volumes = 16x0-0693 = 1-109 1 equ. 0= 1 volume = 1 x 1-108 =1-108 10-527 This sum is almost exactly twice as large as the specific gravity found by direct experiment (i^-2J =5-263); which shows that the relative proportions of the equivalents are correctly given in the empirical formula of camphor. But whether the formula is correct, also, with regard to the absolute number of equivalents, cannot be determined simply from the density of the vapor, because we do not know to how many volumes of camphor vapor 1 equivalent of camphor corresponds. Liebig assumes the equivalent of camphor to correspond to 2 volumes, and gives accordingly the formula C 10 H g ; whilst Dumas assumes it to correspond to 4 volumes, and gives the formula accordingly C 20 H lg O 2 . The knowledge of the density of the vapor affords, therefore, in reality, simply a means of controlling the correctness of the analysis, but not of establishing a rational formula; and although it is made to serve sometimes for the latter purpose, yet this can be done only in the case of substances for which we are able to infer from analogy a certain ratio of condensation : thus, for instance, experience proves that 1 equi- valent of most of the hydrates of the volatile organic acids, of alcohols, &c., corresponds to 4 volumes. In 203, 2, we have deduced the rational formula of hydrated benzoic acid at C 14 H 6 O 4 . Dumas and MUscherlich found the density of the vapor of this acid = 4-26. Now nearly the same number is obtained by dividing by 4 the sum total of the specific gravities of the several constituents contained in 1 equivalent of hydrated benzoic acid, viz., 14 volumes = 11-634 12 volumes H = 0-831 4 volumes O = 4-432 16-897 = 4-224 4 Hermann Kopp ("Compt. rend.," 44, 1347; "Chem. Centralbl.," 1857, 595,) has recently called attention to the fact that, if the equivalent of a substance is calculated upon H = 1, and the density of the vapor of the same upon atmospheric air=l, the division of the equivalent by the density of the vapor gives the following quotients, 474 CALCULATION OF ANALYSES. [ 204. 28-88 14-44 7-22 according as the fonnula corresponds to 4, 2, or 1 volume of vapor : 28-88 corresponds to a condensation to 4 volumes 14-44 2 7-22 1 volume Kopp calls these numbers normal quotients. If the density of the vapor is not quite exact, but only approximate (determined by experi- ment), other numbers are found, but, to be correct, these must come near the normal numbers. If, therefore, we know the equivalent of a body, we may, with the greatest facility, ascertain whether the determination of the density of the vapor of the body has given approximately correct results or not. Gay-Lussac found the density of the vapor of ethyl-alcohol = 1-6133; Dalton = 2-l (Gmdin's " Handbuch der Chemie," 4, 550). Now, which is the correct number? . It is evident that Gay-Lussac's number is approximately correct, for the quotient found by it comes very near the normal quotient, 28 88. Again, if we know the equivalent of a body, and the number of volumes of vapor corresponding to 1 equivalent, we may also, with the same facility, theoretically calculate the density of the vapor of the body. For instance: the equivalent of hydrated benzoic acid is 122. The division of this number by 28'88 gives 4*224, as the density of the vapor, which is the same as that found by actual experiment. And, lastly, if we approximately know (by experiment) the density of the vapor of a body, and also the ratio of condensation, we may, with the aid of these quotients, approximately calculate the equivalent of the body. E.g. The density of the vapor of acetic ether has been found- 3'112. The multiplication of this number by 28 '88 gives 89-87 as the equiva- lent of acetic ether, which comes near the actual equivalent, 88. Having thus shown how the knowledge of the density of the vapor of a body is turned to account as a means of controlling the results of an ultimate analysis of the same, we will now proceed to show how the density of the vapor is calculated from the data obtained as described in 193. We will take as an illustration Dumas's estimation of the specific gravity of the vapor of camphor. The results of the process were as follows : Temperature of the air . . . . 13'5 C. Barometer . . . . 742 millimetres Temperature of the bath at the moment of sealing the globe ..... 244 C. Increase of the weight of the globe 0'70S grm. Volume of mercury required to fill the globe . . . 295 cubic centimetres Residual air 204.] CALCULATION OF ANALYSES. 475 Now, to find the density of the vapor, we have to determine, 1. The weight of the air which the globe holds. (This we must neces- sarily know for the solution of the second question.) 2. The weight of the camphor vapor which the globe holds. 3. The volume to which the camphor vapor corresponds, at C. and 0'7 60 millimetres bar. ^ The solution of these questions is quite simple ; and if the calcula- tion, notwithstanding, appears somewhat complicated, this is merely owing to certain reductions and corrections which are required. 1. The weight of the air in the globe. The globe holds 295 cubic centimetres, as we see by the volume of mercury required to fill it. Now, what is the weight of 295 cubic centimetres of air at 13-5 C. and 0-742 millimetre bar., at C. and 760 millimetres bar. ? The question is solved according to the directions of 198, by the following proportions : 760 : 742:: 295 : x x = 288 cubic centimetres. (At 13-5 C. and 760 milli- metres bar.) and again : 288 288 = 274 1 + (13-5x0-00366) Now 1 cubic centimetre of air at C. and 760 millimetres bar. weighs 0-00129366 grm. ; 274 cubic centimetres weigh accordingly 0-00129366 x 274 = 0-35446 grm. 2. The Weight of the Vapor. At the beginning of the experiment we tared the globe + the air within it ; we afterwards weighed the globe + the vapor (but without the air) ; to find, therefore, the actual weight of the vapor, it is not sufficient to subtract the tare from the weight of the globe filled with vapor, since (glass 4 vapor) (glass + air) is not = vapor; but we have either to subtract, in the first place, the weight of the air from the tare, or to add the weight of the air to the increase of the weight of the globe. Let us do the latter : Weight of air in the globe = 0-35446 grm. Increase of weight of globe = 0-70800 grm. The weight of the vapor is accordingly = 1-06246 grm. 3. The Volume to which this Weight of 1-06246 grm. of Vapor corre- sponds at C. and 760 millimetres bar. We know from the above-given data that this weight corresponds to 295 cubic centimetres at 244 C., and 742 millimetres bar. Before we can proceed to reduce this volume according to the directions of 198, the following corrections are necessary : a. 244 C. of the mercurial thermometer correspond, according to Magnus's experiments, to 239 C. of the air thermometer (see Table VI). 476 CALCULATION OF ANALYSES. [ 204. b. According to Dulong and Petit, glass expands (commencing at C.) 350 00 of its volume for each degree C. The volume of the globe at the moment of sealing was accordingly 295 x 239 295 + - QgQAQ ' = 297 cubic centimetres. If we now proceed to reduce this volume upon C. and 760 milli- metres bar., we find by the proportion, 760 : 742:: 297:* x (i.e. cubic centimetres of vapor at 760 millimetres bar. and 239 C.) = 290 ; and by the equation, 290 1 + (239 x 0-00366) ^ x x (i.e. cubic centimetres of vapor at 760 millimetres bar., and C.) = 154-6. 154-6 cubic centimetres of camphor vapor at 0C, and 760 millimetres bar. weigh accordingly 1-06246 grm. 1 litre (1000 cubic centimetres) weighs consequently 6-87231 grins. ; since 154-6 : 1-06246:: 1000 : 6-87231. Now 1 litre of air at C. and 760 millimetres bar. weighs 1-29366 grm. The specific gravity of the camphor vapor consequently is = 5-312 ; since 1-29366 : 6-87231::! : 5-312. PART II. SPECIAL PART. I. ANALYSIS OP WATERS. A. ANALYSIS OP FRESH WATER IK SPRINGS, WELLS, BROOKS, KIVERS, &c.* 205. THE analysis of the several kinds of fresh water is usually restricted to the quantitative estimation of the following substances. a. Bases : Soda, lime, magnesia. b. Acids : Sulphuric acid, silicic acid, carbonic acid (combined), chlo- rine. c. Mechanically suspended Matters : Clay, &c. We confine ourselves, therefore, here to the estimation of these bodies. In cases where the examination is to extend to other constituents besides these, the methods given in 206 213 are resorted to. I. The Water is dear. 1 . Determination of the Chlorine. This may be effected, either, a, by the gravimetric, or, b, by the volumetric method. a. Gravimetric MetJtod. Take 500 1 000 grammes or c.c.f Acidify with nitric acid, and pre- cipitate with nitrate of silver. Filter when the precipitate has com- pletely subsided ( 141, I., a). If the quantity of the chlorine is so in- considerable that the solution of nitrate of silver produces only a slight turbidity, evaporate a larger portion of the water to ^, ^, ^, &c., of its bulk, filter, wash the precipitate, and treat the filtrate as directed. b. Volumetric Method. Evaporate 1000 grammes or c.c. down to a small quantity of residual liquid, and determine the chlorine in this, without previous filtration, by solution of nitrate of silver, with addition of chromate of potassa ( 141, I., b, a). 2. .Determination of the Sulphuric Acid. Take about 1000 grammes or c.c. Acidify with hydrochloric acid and mix with chloride of barium. Filter after the precipitate has completely subsided ( 132, I., 1). If the quantity of the sulphuric acid is very inconsiderable, evaporate the acidified water to |, , ^, &c., of the bulk, before adding the chloride of barium. 3. Determination of the Silicic Acid, Lime, and Magnesia. Evaporate 1000 grammes of the water best in a platinum dish after * Compare the chapter on the same subject in Fresenius's "Qualitative Analysis," 5th Edition, 208. t As the specific gravity of the fresh water of springs, rivers, &c., differs but little from that of pure water, the several quantities of water may safely be measured instead of weighed. The calculation is facilitated by taking a round number of cubic centi- metres. 480 ANALYSIS OF WATERS. [ 205. addition of some hydrochloric acid, to dryness, treat the residue with hydrochloric acid and water, filter off from the separated silicic acid, and treat the latter as directed 140, II., a. Estimate the lime and mag- nesia in the filtrate as directed 154, 4, a (30)- 4. Determination of the whole Residue and Estimation of the Soda. a. Evaporate 1000 grammes or cubic Centimetres of the water, with proper care, to dryness, in a platinum or porcelain dish, first over a lamp, finally on the water-bath. Expose the residue, in the air-bath, to a temperature of about 356 F., until no further diminution of weight takes place. This gives the total amount of the salts. b. Treat the residue with water, and add, cautiously, dilute sulphuric acid in moderate excess ; cover the vessel during this operation with a dish, to avoid loss from spurting ; then place on the water-bath. After ten minutes, rinse the cover by means of a washing bottle, evaporate the contents of the diah to dryness, expel the free sulphuric acid, ignite the residue, in the last stage with addition of some carbonate of ammonia ( 97, 1), and weigh. The residue consists of sulphate of soda, sul- phate of lime, sulphate of magnesia, and some separated silicic acid. It must not redden moist litmus paper. The quantity of the sulphate of soda in the residue is now found by subtracting from the weight of the latter the known weight of the silicic acid and the weight of the sulphate of lime and sulphate of magnesia calculated from the quantities of these earths found in 3. 5. Direct Estimation of the Soda. The soda may also be determined in the direct way, with comparative expedition, by the following method : Evaporate 1250 grammes or c.c. of the water, in a dish, to about ^, and then add 2 3 c.c. of thin pure milk of lime, so as to impart a strongly alkaline reaction to the fluid ; heat for some time longer, then- wash the contents of the dish into a quarter-litre flask. It is not neces- sary to rinse every particle of the precipitate into the flask ; but the whole of the fluid must be transferred to it, and the particles of the pre- cipitate adhering to the dish well washed, and the washings also added to the flask. Allow the contents to cool, dilute to the mark, shake, let deposit, filter through a dry filter, measure off 200 c.c. of the filtrate, corresponding to 1000 grammes of the water, transfer to another quarter-litre flask, mix with carbonate of ammonia and some oxalate of ammonia, add water up to the mark, shake, let deposit, filter through a dry filter, measure off 200 c.c., corresponding to 800 grammes of the water, add some chloride of ammonium,* evaporate, ignite, and weigh the residual chloride of sodium as directed 98, 3.t 6. Calculate the number found in 1 5 upon 1000 parts of water, and determine from the data obtained the amount of carbonic acid in com- bination, as follows : Add together the quantities of sulphuric acid corresponding to the bases found, and subtract from the sum, first, the amount of sulphuric acid precipitated from the water by chloride of barium (2), and, secondly, * To convert the still remaining sulphate of soda, on ignition, into chloride of sodium. t This process, which entirely dispenses with washing, presents one source of error viz., the space occupied by the precipitates is not taken into account. The error result- ing from this is, however, so trifling, that it may safely be disregarded, as the excess of weight amounts to - 2 per cent, at the most. -205.] ANALYSIS OF WATERS. 481 an amount corresponding to that of the chlorine found (for 1 equiva- lent of Cl, 1 equivalent of SO 3 ) ; the difference expresses the quantity of the carbonic acid combined with the bases in the form of neutral car- bonates. 40 parts of sulphuric acid remaining after subtracting the quantities just stated, correspond accordingly to 22 parts of carbonic acid. If, by way of control, you wish to determine the combined car- bonic acid in the direct way, evaporate 1000 grammes or c. c. of the water, in a flask, until only a small portion is left ; add tincture of lit- mus, then nitric acid of known strength, and proceed as directed 139, I, 6, a, bb. 7. Control. If the quantities of the soda, lime, magnesia, sulphuric acid, silicic acid, carbonic acid, and chlorine are added together, and an amount of oxygen corresponding to the chlorine (since this latter is combined with metal and not with oxide) is subtracted from the sum, the balance re- maining must nearly correspond to the total amount of the salts found in 4, a. Perfect correspondence cannot be expected, since, 1, upon the evaporation of the water chloride of magnesium is partially decomposed, and converted into a basic salt ; 2, the silicic acid expels some carbonic acid ; 3, it is difficult to free carbonate of magnesia from water without incurring loss of carbonic acid ; and. 4, the residue remaining upon the evaporation of the water contains the carbonate of magnesia as a basic salt, whereas, in our calculation, we have assumed the quantity of car- bouic acid corresponding to the neutral salt. II. The water is not clear. Fill a large flask of known capacity with the water, close with a glass stopper, and allow the flask to stand in the cold until the siispended matter is deposited ; draw off the clear water with a siphon as far as practicable, niter from the residual sediment, dry or ignite the contents of the filter, aud weigh. Treat the clear water as directed in I. Respecting the calculation of the analysis, I refer to 213, remarking simply that it is usually* arranged upon the following principles : Chlorine is calculated in combination with the sodium ; if there is an excess, this is calculated in combination with the magnesium ; if there is still an excess, this is calculated in combination with the calcium. If, on the other hand, there remains an excess of soda, this is calculated in combination with sulphuric acid. The sulphuric acid, or, if part of this has been calculated already in combination with soda, the remainder of it, is estimated in combination with lime. The silicic acid is put down in the free state, the remainder of the lime and the magnesia as car- bonates, and this, according to circumstances, either as neutral carbonates or as bicarbonates. It must always be borne in mind that the results of the qualitative analysis may render another arrangement of the calculation necessary. In the statement of the results, the quantities are often calculated for 10,000 parts of water instead of 1000 parts ; and frequently also in grains per pound of water (1 pound = 7680 grains). For technical purposes, it is sometimes* sufficient to estimate the harcl- * There is a certain latitude allowed in the mode of arranging the results of an analysis. II. I I 482 ANALYSIS OF MINERAL WATERS. [ 206. 'ness of the water (the relative amount of liine and magnesia in it) by means of a solution of soap of known strength. A detailed description of this method, which was first employed by Clark, has been given by Fehling and Faiszt (Gewerbeblatt aus Wiirtemberg, 1852, 193 ; " Pharmaceut. Centralbl.," 1852, 513). It is only by strict adhex-ence to the rules there given that accurate and corresponding results are ob- tained by this method. B. ANALYSIS OF MINERAL WATERS.* 206. In the analysis of mineral waters we have a larger number of sub- stances than claim our attention in that of fresh waters. In general, the following substances have to be quantitatively determined in the analysis of a mineral water : a. Bases : Potassa, soda, lithia, ammonia, lime, baryta, strontia, magnesia, alumina, protoxide of iron, protoxide of man- ganese (oxide of zinc, protoxide of nickel, t protoxide of cobalt,t oxide of copper, oxide of lead, binoxide of tin, teroxide of antimony). b. Acids : Sulphuric acid, phosphoric acid, silicic acid, carbonic acid, boracic acid, nitric acid, hyposulphurous acid, chlorine, iodine, bromine, fluorine, hydrosulphuric acid, crenic acid, apocrenic acid, formic acid, propionic acid, &c. (arsenious and arsenic acids, titanic acidt). c. Non-combined elements and indifferent gases : Oxygen, nitrogen, light carbide of hydrogen. d. Indifferent organic matters. Many of these substances occur in most springs, in considerable pro- portions ; of the bases, more particularly soda, lime, magnesia, and some- times also protoxide of iron ; and of the acids, sulphuric acid, carbonic acid, silicic acid, chlorine, and sometimes also hydrosulphuric acid. The others are almost invariably found only in trifling and often in exceed- ingly minute proportions. The substances between brackets occur usually only in the muddy, ochreous, or solid sinter deposits, + which form, in most mineral springs, in the parts where the air acts upon the water flowing off, or kept in a reservoir. The subject of the analysis of mineral waters is properly treated under two heads, viz., 1. The analytical process : and, 2. The calculation and arrangement of the results. 1. THE ANALYTICAL PROCESS. The performance of the analytical process is divided into two parts, viz., 1, operations and experiments at the spring or well ; and, 2, opera- tions and experiments in the laboratory. * Compare the chapter on the same subject in Freseniuss " Qualitative Analysis," 5th Edition, 209. t Mazade, Henry ("Journ. de Pharm. et de Chim.," 3 se'rie, 24, 305 ; " Journ. f. prakt. Chem.," 62, 29). J If they contain oxide of lead, oxide of copper, &c., which might proceed from metal tubes, stopcocks, &c., the real origin of the oxides must be most carefully ascertained (see " Qualitative Analysis"). 207.] ANALYSIS OF MINERAL WATERS. 483 A. OPERATIONS AND EXPERIMENTS AT THE SPRING OR WELL. I. APPARATUS AND OTHER REQUISITES. 207. 1. A pipette of 2 00 cubic centimetres capacity. Fig. 131 represents a pipette in a travelling case, as recommended by Fr. Mohr. A common siphon may also be used instead, with the lower orifice somewhat narrow. The capacity of this is ascertained by filling it with water, and measuring the contents in a graduated glass. 2. Four bottles with well-fitting corks; each of these bottles should hold about 300 c.c. 3. An accurately graduated thermometer, with plain scale. 4. A mixture of 2 volumes of solution of ammonia and 1 volume of solution of chloride of calcium or chloride of barium ( 139, I., 6, a). This mixture is boiled. It is filtered at the spring or well. 5. About 8 white glass bottles of 1 2 litres capa- city, with well-fitting stoppers ; ground-glass stoppers answer the purpose best. If corks are used, it is advisable to cover them with a thin piece of vulcanized india-rubber. 6. Some larger bottles, holding together at least 50 pounds of water, with well-fitting corks or glass- stoppers ; instead of these a small carboy may be used. 7. A litre and a half-litre flask. 8. 1 middle-sized and 2 large funnels. 9. Swedish filtering paper. 10. Flasks, beakers, lamp, glass rods, glass tubes, Fig. 131. caoutchouc tubes, files, scissors, knife, corks, string, &c. 11. Reagents, more especially the following: ammonia, hydrochloric acid, acetic acid, nitrate of silver, chloride of barium, oxalate of ammonia, tannic acid and gallic acid (or infusion of galls), tincture of litmus (freshly prepared), test papers. Besides these articles, the following are also re- quired under certain circumstances : a. If the Water contains Sulphuretted Hydrogen or an Alkaline Sulphide. 12. A solution of known strength of iodine in iodide of potassium. This must be very dilute ; the best way is to prepare it by adding to 1 volume of Bunseris solution of iodine ( 14G, 1) 4 volumes of water; which gives a mixture containing in 1 c.c. about O'OOl grm. of iodine. 13. Starch. 14. A burette with compression clamp, and several pipettes. 15. A solution of arsenious acid in hydrochloric acid, or of arsenite of soda; also the reagents and apparatus mentioned in 208, 9. b. If the Water contains a large proportion of Protoxide of Iron, which it is intended to estimate volumelricatty at the Spring or Well. 16. A solution of permanganate of potassa. For waters abounding in iron, this solution must be of such a degi'ee of dilution that 100 c.c. of it convert about O'l grm. of iron from the state of protoxide to that of I X j 484 ANALYSIS OF MINERAL WATERS. [ 207. sesquioxide. If the water contains only a moderate proportion of iron, the solution must be still more largely diluted. As it is necessary to fix the strength of the solution on the spot, a burette, a pipette, and weighed pieces of pianoforte wire, or a standard solution of oxalic acid ( 112, b, 2, cc), are also required. c. If it is intended to determine the wliole of the Gases dissolved in the Water. 17. A glass globe closed by a caoutchouc plate ; also a long gutta-percha tube with brass stopcock or caoutchouc valve (for the latter, see 185, b). 18. Another caoutchouc valve of greater width ; the width of the caoutchouc tube must correspond to that of the neck of the globe (17). 19. An ebullition globe. 20. A graduated gas receiver, and 21. Several non-graduated gas-receivers, properly arranged for sealing. 22. A blow-pipe for sealing. To give the operator the free use of both hands, Bunsen recommends the ar- rangement shown in Fig. 132. (a) is a small lamp, holding about 3 grammes of oil ; this is attached to the blow-pipe, by means of a somewhat flexible wire with ring (b), through which the nozzle of the blow-pipe passes. The proper position is given to the flame by bending the wire. The cork (c) serves as mouth-piece, to enable the operator to hold the ap- paratus between the teeth. Fora more detailed description of the other apparatus (17 21), see 208. d. Jf it is intended to determine tlie free Gases evolved at the /Spring or Well. 23. A number of test-tubes, holding 40 60 c.c. each (see Fig. 133), (a) drawn out in the blow-pipe flame to the thickness of a small straw, Fig. 133. Fig. 134. 208.] ANALYSIS OF MINERAL WATERS. 485 and connected air-tight with a funnel as shown in the drawing. They are intended to collect the gases at the spring, for subsequent examin- ation in the laboratory. For the collection of large quantities of gas. bottles, with the neck drawn out (Fig. 134), are used instead of test-tubes. 24. A long glass tube of such small diameter, that it may be passed through the drawn-out narrowed parts of the tubes or bottles described in 23. 25. In cases where it is intended simply to estimate gases absorbable by solution of potassa (carbonic acid, sulphuretted hydrogen), without determining the other gases, which are not absorbed by that agent, only a graduated tube, some solution of potassa, and a small funnel are required. If the water evolves sulphuretted hydrogen, the analyst must provide himself, in addition to the above enumerated articles, with, 26. A flask with the neck somewhat drawn out, and provided with a caoutchouc tube and compression clamp ; and, 27. An ammoniacal solution of chloride of copper (see 208, 14). II. ANALYTICAL PROCESSES. 208. 1. Examine the appearance (color, clearness, /3), or by sulphide of ammonium, 159 (54)- Test the filtrate for lime, and after this for magnesia. If traces of these substances are found, collect them on small filters, and ignite these jointly with the filters containing the principal bulk of the same substances (see 6). Instead of precipitating the man- ganese with chlorine or sulphide of ammouinm, you may also add a little chloride of zinc to the fluid, then precipitate with carbonate of soda, and determine the manganese in the ignited residue as directed in 159 (59)- Precipitate now the solution remaining in the flask with ammonia and sulphide of ammonium, and determine in the filtrate the traces of lime and magnesia which may be present. Instead of employing this process, the iron and manganese can be determined directly by the volumetrical method ; first the manganese as directed 160 (92)> then the iron in the residue. b. From the filtrate, precipitate the lime with oxalate of ammonia, deter- mine the lime by adding a sufficient quantity of pure oxalate of ammonia quite free from potassa and soda ( 154, 30)- The weighed precipi- tate must be carefully tested for magnesia; if any of that earth is found, this must be determined separately, and subtracted, as pure magnesia, from the weight of the carbonate of lime containing magnesia. Evaporate the fluid filtered off from the oxalate of lime in a porcelain dish to dryness, and heat the residue gently in a platinum dish ( 42), to remove the ammonia salts. In the residue, separate the magnesia finally from the alkalies as directed 153 (18). Dissolve the separated mag- nesia in hydrochloric acid, add ammonia, and precipitate as phosphate of ammonia and magnesia. By this course of proceeding, you avoid those mistakes which are so apt to arise from the presence of silicic acid and alumina, proceeding from the vessels used in the process. The chlorides of the alkali metals must, after weighing, be examined as to their purity (see 152, 1, a, foot-note). If the quantity of the sulphuric acid was small, the solution of the alkaline chlorides is free from that acid, since the trifling amount of sulphate has been decomposed by the ignition with chloride of am- monium. But as this can never be positively known, and as repeated evaporation with chloride of ammonium is somewhat tedious, the follow- ing proceeding may be adopted : transfer a few drops of the solution of the weighed pure chlorides of the alkali metals, by means of a glass rod, to a test tube, and add a few drops of alcoholic solution of chloride of strontium and a little spirit of wine. If no precipitate forms, this is a proof that the fluid contains no sulphuric acid, in which case add the contents of the test tube again to the solution, and determine the potassa in the latter as directed 152 (2). But if a precipitate forms, treat the whole solution cautiously in the same way as the sample in the test tube; let the mixture stand some time, and then filter the fluid off from the precipitated sulphate of strontia, which determine as directed 102. Estimate the potassa in the filtrate as directed 152 (2). It is necessary to weigh the sulphate of strontia, that the quantity of the soda may be accurately calculated. The quantity of the soda is ascertained by sub- tracting from the weighed residue in the dish, 1, the chloride of potas- sium, and, 2, the weight of sulphate of soda corresponding to the 496 ANALYSIS OF MINERAL WATERS. [ 209. sulphuric acid found. The remainder is chloride of sodium. The soda is then calculated from the sulphate of soda and chloride of sodium. The foregoing method may in many cases, more particularly in presence of traces of manganese, be simplified, by mixing the fluid filtered off from the silicic acid at once with ammonia free from carbonic acid, filtering the precipitate, washing, redissolving in hydrochloric acid, and precipi- tating the solution again with ammonia. The precipitate so obtained is dried, ignited, weighed, redissolved in hydrochloric acid, the silicic acid, which may be left, determined, and the iron in the solution finally estimated volumetrically, by way of control. In presence of alumina and phosphoric acid the results of the volumetric determination are taken to be the more accurate. If you wish to ensure the precipitation of the manganese along with the iron, add to the solution hypochlorous acid, or chlorine water, before proceeding to precipitate. It is often also preferred to determine only the lime and magnesia (as directed 154, 30) in the fluid filtered off from the sesquioxide of iron, and to estimate the alkalies in a separate portion of the water. For this purpose, about 500 1000 grammes of the water are boiled with pure milk of lime, best in a silver dish, then filtered, the filtrate concentrated, the lime precipitated by carbonate and a little oxalate of ammonia, filtered off, and the alkalies in the filtrate determined as chlorides. If the water contains only a small proportion of sulphuric acid, it suffices in evaporating the fluid containing the alkalies, to add, towards the end of the process, some chloride of ammonium ; but, if the proportion of sulphuric acid present is large, it is necessary to add at once, before the addition of the milk of lime, a quantity of chloride of barium equivalent to the known amount of the sulphuric acid. In this process also, proper attention must be paid, as regards the chlorides of the alkali metals, to the remarks in the foot-note to 152, 1, a. 5. ESTIMATION OF THE LIME, MAGNESIA, IRON (AND MANGANESE), IN THE PRECIPITATE FORMED ON BOILING THE WATER ; AND OF THE LIME AND MAGNESIA IN THE BOILED WATER, Boil 500 1000 grammes of the water in a glass flask for about 3 hours, replacing the evaporated water from time to time by distilled water. (If this precaution were neglected, sulphate of lime might separate in conjunction with the carbonates of the alkaline earths.) Filter the precipitate and wash. Separate and determine the lime and laaguesia in the filtrate as directed 154 (30). Dissolve the precipitate in dilute hydrochloric acid, heat with some nitric acid, and determine the iron (manganese), lime, and magnesia in the solution as in 4- This course of proceeding will enable the operator to judge how much of the lime and magnesia is present as bicarbonate. However, it must not be lost sight of, that the simple carbonates of lime and magnesia are not altogether insoluble in water, and, to be as nearly accurate as possible, proper correction must accordingly be made for this in the calculation. 6. ESTIMATION OF THE TOTAL AMOUNT OF CARBONIC ACID PRESENT. The bottles filled at the spring, as stated 208, 8, are employed for the purpose. The determination is effected, in 2 or 3 bottles, exactly as directed 139, I., b. The results must pretty nearly agree; the mean 209.] ANALYSIS OF MINERAL WATERS. 497 of them is taken. If the water which has given the baryta or lime precipitates, has been measured, the number of cubic centimetres must be multiplied by the specific gravity found, to ascertain the number of grammes of water to which the carbonic acid corresponds. 7. ESTIMATION OF THE BARYTA, STRONTIA, LITHIA, PROTOXIDE OF MANGANESE, ALUMINA, AND PHOSPHORIC ACID; AND ALSO OF THE IODINE AND BROMINE. The residue left upon evaporating 10,000 20,000 grammes of the water (see the beginning of this paragraph), is used to effect the deter- mination of these substances, which are present only in small propor- tions. Triturate and heat the perfectly dry saline mass repeatedly with spirit of wine of 96 per cent., until you are quite sure that the iodides and bromides of the alkali metals which may be present are completely dissolved. a. Add to the alcoholic filtrate 2 drops of pure solution of potassa, and distil, in a flask, on the water-bath, to dryness, boil the residue repeatedly with absolute alcohol, distil the filtrate, after addition of a drop of pure potassa solution, again to dryness, and ignite the residue very gently, to destroy the organic matter which may be present. The trifling residual saline mass is treated best as directed 169 (227)? niore especially when there is some uncertainty as to the presence of iodine ; since this course of proceeding leads not only to the detection of the latter substance, but also to its determination and separation, so that the bromine may also afterwards be determined. For the details of the process, I refer to 1 69, 3 (226 229), where the subject has been fully treated. As traces of lithia may have passed into the alcoholic solution, remove, after the precipitation of the bromine, the excess of silver from the filtrate, by means of hydrochloric acid, and add this solution as well as the residual saline mass left upon boiling the residue of the first dis- tillation with absolute alcohol, which consists chiefly of chloride of sodium, to the principal residue of the mineral water. 6. Treat the total residue left, upon boiling with alcohol, with water, add hydrochloric acid, cautiously, until the solution is acid, and then evapor-ate to dryness. Dissolve the saline mass in water, with addition of very little hydrochloric acid, add an equal volume of alcohol,* allow the mixture to stand for 2-i hours, and then filter off the fluid from the undissolved residue, which, besides silicic acid, must contain all the baryta and strontia present, in the form of sulphates, and generally contains also sulphate of lime. aa. Wash an d dry this residue, and, after adding the filter ash, boil with carbonate of soda and solution of soda, to dissolve the principal portion of the silicic acid. Fuse the undissolved part with some car- bonate of soda and potassa, and treat the fused mass with boiling water, until no trace of sulphuric acid can be detected in the washings. Dis- solve the residue which must contain baryta and strontia in the form of carbonates in a very small proportion of dilute hydrochloric acid, and separate the baryta, strontia, and lime, as directed 154 (26)- bb. Oxidize the fluid filtered from the silicious residue, after evaporating * Sulphate of strontia is slightly soluble in aqueous solution of chloride of sodium. II. K K 498 ANALYSIS OF MINERAL "WATERS. [ 209. the alcohol, with nitric acid, nearly neutralize it with absolutely pure carbonate of soda or potassa (quite free from phosphoric acid), and then precipitate with perfectly pure carbonate of baryta (free from lime, strontia, and phosphoric acid). Let the mixture stand in a stoppered flask for 12 hours in the cold, then filter, and wash the precipitate thoroughly. a. Heat the precipitate which, besides the excess of carbonate of baryta and sulphate of baryta, contains all the sesquioxide of iron, and also alumina* and phosphoric acid, and may contain, besides, traces of fluoride of calcium with hydrochloric acid, and throw down the baryta from the solution by sulphuric acid added very slightly in excess. Eva- porate in the water-bath, to remove the excess of hydrochloric acid as far as practicable ; dissolve the residue in water, transfer the solution to a small flask, add tartaric acid, then ammonia, and allow the fluid to stand 12 hours. If a trifling precipitate subsides, filter and examine this ; it may contain fluorinet and phosphoric acid in combination with lime. Mix the clear or filtered fluid with sulphide of ammonium, and let the mixture stand in a stoppered flask until the fluid exhibits a pure yellow color. Filter from the sulphide of iron, and evaporate the filtrate in a platinum dish, adding some pure carbonate of soda that there may be an excess of fixed base for the phosphoric acid and some pure nitrate of potassa, the more readily to destroy the tartaric acid. Finally heat to redness until the residue looks perfectly white. Then add water and hydrochloric acid until complete solution is effected,! au( ^ precipitate the clear fluid with ammonia. If a precipitate forms (hydrate of alu- mina, or phosphate of alumina, or a mixture of both), filter and weigh. Mix the filtrate with a little sulphate of magnesia. If this gives a pre- cipitate of phosphate of magnesia and ammonia (which determine as directed 134, I., b), the alumina precipitate may be entered in the cal- culation as phosphate of alumina (Al a O 3 , P O 5 ). But if no precipitate forms, the phosphoric acid in the alumina precipitate has to be deter- mined as directed 134, L, b, ft. I have to remark here, once more, that the alumina found can only be calculated as an ingredient of the analysed water, if the processes of evaporation, &c., have been conducted in plati- num or silver vessels. ft. Mix the fluid filtered from the precipitate produced by carbonate of baryta, in a stoppered bottle, with chloride of ammonium, ammonia, and sulphide of ammonium. Let the mixture stand 12 hours, and then filter the precipitated sulphide of manganese ; dissolve it in hydrochloric acid, heat, throw down by a little sulphuric acid the trace of baryta which is generally still present, then add, without filtering off the pre- cipitate, ammonia and sulphide of ammonium, let the mixture stand 12 hours, filter, wash, treat the precipitate with hydrochloric acid, filter again, and determine finally the manganese as directed 109, 1, a. Or, mix the hydrochloric acid solution of the first precipitate of sulphide of * If the evaporation of the 10,000 or 20,000 grammes of the water has been con- ducted in a porcelain dish, the residue left upon that evaporation (and accordingly also the fluid of bb, and the precipitate thrown down from it) contains, besides the alumina originally present in the water, also alumina derived from the porcelain evaporating dish. t As the greater portion of the fluorine has, in the evaporation with hydrochloric acid,, volatilized as fluoride of silicon, the fluorine found in a gives, of course, no clue to the proportion of that element contained in the water. * The operation of heating this residue (which contains nitrate of potassa) with hydro- chloric acid, must not be conducted in a platinum dish. 209.] ANALYSIS OF MINERAL WATERS. 499 manganese with some chloride of barium, precipitate with carbonate of soda, and determine the manganese by the volumetrical method as directed 159 (59). In the fluid filtered from the sulphide of manganese, there still remains the lithia to be deteraiined. To effect the determination of this substance, mix the filtrate with ammonia and carbonate of ammonia, allow to de- posit, and filter the fluid from the carbonate of lime and baryta. Evapo- rate the filtrate to dryuess, and remove the chloride of ammonium by gentle ignition ; then, to remove the magnesia, boil the residue with water, with addition of a little pure milk of lime, filter, remove the ex- cess of lime, cautiously, with ammonia, carbonate and some oxalate of ammonia, filter, evaporate the filtrate to dryness, remove the ammonia salts by ignition, and treat the residue with a mixture of absolute alco- hol and anhydrous ether, with addition of a few drops of hydrochloric acid.* If chloride of lithium is present, it will dissolve in this mixture. Evaporate the solution, dissolve the residue in water, and test the mode- rately concentrated solution with ammonia and carbonate of ammonia. If the slightest turbidity is perceptible, the same operation must be re- peated, to remove the still remaining traces of baryta, lime, or magnesia. Evaporate again to dryness, ignite gently, treat the residue once more with absolute alcohol and ether, with addition of a little hydrochloric, acid, and filter if anything is left undissolved ; evaporate the solution, and determine the lithia finally as directed 152 (7). 8. ESTIMATION OF THE AMMONIA, To effect the estimation of the ammonia in mineral waters, I can re- commend the following method, which I have employed with good result* in my analysis of the Wiesbaden KocJibrunnen, : Evaporate about 2000 grammes of the mineral water, with addition of a small measured amount of dilute hydrochloric acid, in a tubulated retort, until only a small quantity of the fluid is left. Add to this, through a funnel-tube, a measured quantity of freshly prepared solution of soda, put the neck of the retort a little upwards, and keep the con- tents boiling until the fluid is almost entirely evaporated. Conduct the whole of the vapors escaping through a Liebig's condensing apparatus, and receive the distillate in a flask containing a little water acidified with a small measured quantity of hydrochloric acid. Convert the chloride of ammonium contained in this fluid into ammonio-bichloride of platinum, by evaporation with a measured quantity of bichloride of platinum ( 99, 2). Makonow a counter-experiment with the same quantities of hydrochloric acid, solution of soda, and bichloride of platinum, and de- duct the small amount of ammonio-bichloride of platinum obtained in this, from that found in the first experiment : the difference expresses the quantity proceeding from the analysed water. Instead of this method, you may also employ the more simple process which Boussingault has lately proposed (" Compt. rend.," 36, 814 ; " Pharm. Centralblatt," 1853,369), and which is conducted as follows : Distil, in a distilling apparatus, about 10 litres of the water, until about f have passed over. In the analysis of saline springs, you must add some solution of soda or milk of lime to ensure the ammonia passing over. Transfer the distillate to a glass flask connected with a Liebig's * Chloride of lithium is rendered basic even by gentle ignition, 152 (7). K K 2 500 ANALYSIS OP MINERAL WATERS. [ 209. condensing apparat us, and distil i over. Determine the ammonia in this distillate by adding 5 or 10 c.c. of very dilute sulphuric acid, and satxi- ratiug the excess of the latter by a solution of soda, of which 5 c.c. neutralize 1 c.c. of the dilute sulphuric acid used (comp. 99, 3). Let another ^ distil over, and determine the ammonia in this (if any is still present) in the same way. But the first portion usually contains the whole of the ammonia. 9. DETERMINATION OF THE NITRIC ACID. Evaporate a rather large quantity of the water with an excess of pure carbonate of soda, filter the precipitate formed, wash, evaporate the filtrate to dryness, mix the residue uniformly, weigh, and determine in weighed portions of it the nitric acid by Pelouze's method modified by ine ( 149, II., a). 10. DETECTION AND ESTIMATION OF THE CRENIC AND APOCRENIC ACIDS. Boil a rather large quantity of the precipitate formed upon the evapo- ration of the water, about 1 hour, with solution of potassa ; filter, acidify the filtrate with acetic acid, add ammonia, and, after 12 hours, filter off the precipitate of silicic acid and alumina, which usually forms. Add to the filtrate acetic acid to acid reaction, then neutral acetate of copper. If a brownish precipitate forms, this consists of apocrenate of copper (which, according to Mulder, contains variable quantities of ammonia) ; an analysis of apocrenate of copper dried at 284 F., gave 42'8 per cent, of oxide of copper. Mix the fluid filtered from the precipitate with carbonate of ammonia, until the green color is changed to blue ; then apply a gentle heat. If a bluish-green precipitate forms, this is crenate of copper, which, dried at 284 F., contains 74'12 per cent, of oxide of copper (Mulder).* 11. DETECTION AND ESTIMATION OF OTHER NON- VOLATILE ORGANIC MATTERS. Almost all mineral waters contain non- volatile organic matters, even though only in very small proportions. Many of them are of a resinous nature, in which case they pass into the alcoholic solution of the residue of the mineral water ; from this solution they separate upon distillation, with addition of some water in the last stage of the process. If pre- sent, they may be quantitatively determined, on the occasion of the estimation of the iodine and bromine ( 209, 7, a). fA_nother class of organic matters do not dissolve in alcohol, but are obtained in solution, if the residue of the mineral water is boiled with water. If it is wished to determine the weight of these organic matters, which are usually, for want of a more accurate knowledge of their nature, called extractive matters, the aqueous extract of the residue of the mineral water, exhausted by alcohol, is evaporated with carbonate of soda to dryness, the residue boiled with water, the solution filtered, the filtrate evaporated to dryness, and the residue dried at 284 F., until it suffers no further diminution of weight. It is then gently ignited until the black color which it at first acquires has disappeared. The difference between * For more detailed information on the subject of crenic acid and apocrenic acid, I refer to Mulder's paper on these acids in the "Journal f. prakt. Chem.," 32, p. 321. 209.] ANALYSIS OF MINERAL WATERS. 501 the weight of the dried and that of the ignited residue indicates the amount of the extractive matter. Small quantities of organic matters. are occasionally still left in the residue of the mineral water after ex- hausting with alcohol and with water. If it were attempted to deter- mine these by the difference between the weight of the residue dried at 284 F., and that of the ignited residue, a very inaccurate result would be arrived at, as, under these circumstances, to name only one source of error, carbonate of magnesia loses its carbonic acid. 12. DETECTION AND ESTIMATION OF VOLATILE ORGANIC ACIDS. Scherer (" AnnaL d. Chem. u. Pharm.," 99, 257) found, in his analysis of the mineral springs of Briickenau, in Bavaria, also butyric acid, pro- pionic acid, acetic acid, and formic acid substances which had not before been observed in mineral waters. Soon after, I also found traces of the same acids in the sulphur spring of Weilbach (" Journ. f. prakt. Chem.," 70, 15). If it is intended to examine a mineral water for these acids, the water must be used quite fresh, since otherwise the volatile organic acids detected afterwards might be products of subsequent processes of decomposition. The following is tidterer's process for determining these volatile organic acids : Evaporate a rather large quantity of the mineral water, and filter the fluid off from the precipitate formed ; if the water contains no alkaline bi- carbonate, add carbonate of soda to alkaline reaction, before proceeding to evaporate. Acidify the concentrated mother-liquor with sulphuric acid, with proper caution, and precipitate the chlorine by sulphate of oxide of silver, taking care to have rather a slight excess of chlorine than of silver. Filter, distil the filtrate until the fluid passing over no longer shows acid reaction, saturate the distillate with baryta water, remove any excess of baryta by carbonic acid, boil, concentrate, filter, evaporate to dryness, in a weighed dish, dry at 212 F., and weigh the residue, which contains the volatile organic acids in combination with baryta. Extract the residue with warm spirit of wine, which leaves the formate of baryta undissolved. After drying and weighing the latter, test it with solution of nitrate of silver and chloride of mercury. Evaporate the alcoholic solution of the other baryta compounds at a gentle heat, dissolve the larger portion of the residue in a copious amount of water, and precipitate the baryta from the solution by sulphate of oxide of silver, with proper caution. Let the fluid filtered off from the precipi- tate evaporate under the exsiccator. As soon as a sufficient quantity of silver salt has crystallized, remove the crystals from the fluid, dry over sulphuric acid, and employ the dry salt for the determination of the equivalent. Evaporate finally the rest of the fluid over sulphuric acid, press the salt between sheets of blotting paper, dry over sulphuric acid, and analyse the salt. By way of control, determine, by means of sulphuric acid, the baryta in another portion of the residue left upon the evaporation of the alco- holic solution of the baryta salts. In this process the presence of the volatile fatty acid (propionic acid, butyric acid, &c.) may be detected by the characteristic odor of the acid. If the fluid is sufficiently con- centrated, and has been allowed to stand at rest for some time, the microscope will also occasionally show minute fatty drops floating on the surface. 502 ANALYSIS OF MINERAL WATERS. [ 210. 13. As regards BOEACIC ACID and FLUOBINE,* the simple detection of these substances is generally sufficient for the purposes of the analysis of a mineral water. For their quantitative determination in exceptional cases, I refer to the General Part. 14. EXAMINATION OF THE GASES. 210. To examine the gases collected at the spring (see 208, 11 and 12), and brought to the laboratory in sealed tubes, take a graduated tube of the form described in 12, and illustrated in Fig. 2, moisten the inside with a drop of water, and then fill with mercury, f Immerse the tube con- taining the gas in the mercurial trough, break off the point, and, by giving the proper inclination, cause the gas to ascend into the graduated tube. Read off the volume of the gas, with due regard to the temperature and atmospheric pressure ; then introduce into the gas, by means of a plati- num wire, on which it is cast, a ball of hydrate of potassa,| moistened with water. Take care not to allow the other end of the wire to pro- ject above the surface of the mercury, otherwise a diffusion of the con- fined gas with the atmospheric air will take place along the Avire, which is not moistened by the mercury. When the volume of the gas shows no further diminution, replace the moist potassa ball by a dry one, remove this also after an hour, and then read off the volume of the gas. The gas absorbed consists of carbonic acid, and, in cases where sulphu- retted hydrogen is present, also of the latter gas, which, however, has already been determined ; still, the sulphide of potassium in the potassa ball may be estimated as directed 148, II., 2, c. The gaseous residue consists usually only of oxygen and nitrogen, in which case it may be examined as directed in the chapter on the Analysis of Atmospheric Air ( 267). If there is reason to suspect the presence of marsh gas, the oxygen is removed by means of a well-wetted ball of phosphorus|| introduced into thegaseous mixture, and left in contact with it in a moderately warm place, as long as white fumes of phospho- rous acid are visible round the ball. If no fumes are visible at 59 77 F., this must not be looked upon as a proof of the absence of oxygen, as the presence of carbides of hydrogen prevents the slow combustion of the phosphorus. In such cases, the phosphorus ball occasionally requires heating near to the fusing point, to bring about the absorption of the oxygen (Bunsen). The phosphorous acid fumes, the tension of which cannot well be taken into account, are ultimately absorbed by a moistened potassa ball ; the gas is then dried by means of a ball of hydrate of potassa, and finally measured in the dry state. Instead of a phosphorus ball, a ball of papier-mache" may be employed to effect the removal of * For the detection of fluorine, compare /. Nickl&s (" Coiiipt. rend.," 1857, 44, 679 ; " Journ. f. prakt. Chem.," 71, 383). Nickles recommends to free the sulphuric acid most carefully from fluorine before using it, and to substitute a plate of rock crystal for the glass plate usually employed. t See 184, aa, footnote. J Which, besides the hydration water, contains also still water of crystallization. Balls of this kind are made by pouring fused crystallized hydrate of potassa into a bullet-mould of about six millimetres inner diameter, into which a platinum wire is inserted, with the end reaching into the middle. After cooling, the ball is found attached to the wire. The neck which has formed on the wire is scraped off with a knife. II Cast on a platinum wire, under warm water. 210.] ANALYSIS OP MINERAL WATERS. 503 the oxygen ; this papier-mache ball must be moistened with a concen- trated alkaline solution of pyrogallate of potassa, and, if required, be re- placed, after some time, by a second ball. After this operation, the gas is dried by means of a ball of hydrate of potassa. Bunsen prefers the use of a papier-mache instead of a phosphorus ball. The composition of the gaseous residue, which generally consists either of nitrogen alone, or of nitrogen plus marsh gas, is now ascertained by transferring it, wholly or partially, to a eudiometer ( 12, Fig. 1), mixing with 812 vols. of air and 2 vols. of oxygen to guard against the formation of nitric acid and trying to explode the gaseous mixture. Should this fail, electrolytic detonating gas is added to the extreme limit of combus- tibility, the carbonic acid generated re-absorbed, the marsh gas calculated from this, and the nitrogen found by the difference. For the details of the process, I refer to Banserfs "Gasometry," translated by Roscoe, a work which ought to be in the hands of every one engaged in the analysis of gases. To ascertain whether the gaseous residue left after the absorption of the carbonic acid and the oxygen, contains carburetted hydrogen, I have often successfully employed the following method : Insert one limb of a U-shaped narrow glass tube into the cylinder containing the gaseous residue, which is confined over water ; connect the other limb with a piece of india-rubber tubing, closed by means of a valve. Arrange now the following apparatus : Pour some solution of potassa into a small TJ-shaped tube, connect the outer limb of this with a little tube bent at a right angle, which bears a small piece of india-rubber tubing closed by a compression clamp. Connect the other limb with a second small U-shaped tube, filled with hydrate of potassa, and this again with a thin combustion tube, 2 deci- metres long, filled in the middle with a rather close-packed layer, about 8 centimetres long, of fine copper turnings strongly oxidized by ignition in oxygen gas. Connect the other end of the combustion tube with a somewhat larger U-shaped tube, containing lime water, and this again with a hydrate of potassa tube ; connect the latter finally with an aspi- rator. Open the cock of the latter, and observe whether the joinings are air-tight ; if they are, heat the copper turnings, by means of two gas lamps, to ignition, open the compression clamp cautiously, and let a slow current of air pass through the apparatus for 5 minutes. This should not impart the least turbidity to the lime water ; if the lime water is rendered turbid, replace it by a fresh portion, after the first ignition, and repeat the experiment. If the lime water remains clear, connect, by means of a small glass tube, the india-rubber tubing which is closed by a valve, with that closed by a compression clamp. As the former, which closes the bent tube inserted into the cylinder, remains closed, no more air bubbles can pass through the apparatus. Open now the valve a little, and allow the gas of the cylinder to enter very slowly. The quantity of gas is generally so small that it is entirely absorbed in the first U-shaped tube. When all the gas is absorbed, allow also some water to enter, and clo.se the valve only when the water just makes its appearance in the little glass tube behind it. Now close the clamp, disconnect the india-rubber tube with the valve, and, opening the clamp a little, allow a very slow current of air ti pass for a sufficient length of time over the ignited oxide of copper. This current of air carries along with it the gas which has previously 504 ANALYSIS OF MINERAL WATERS. [ 211. entered ; if this contains carburetted hydrogen, the lime water is ren- dered turbid, owing to the formation of carbonate of lime. If the tur- bidity is sufficiently marked, the quantity of the carbonate of lime may be determined, and the amount of marsh gas calculated from the result. MODIFICATIONS REQUIRED BY THE PRESENCE OF A FIXED ALKALINE CARBONATE. 211. 1. A mineral water containing an alkaline carbonate, cannot contain soluble salts of lime and magnesia ; all the lime and magnesia found in it must, therefore, be regarded as carbonates dissolved by the agency of free carbonic acid, although the whole of the magnesia does not precipi- tate upon boiling the water, a small quantity of a double carbonate of soda and magnesia being invariably formed under these circumstances. The separate determination of the lime and magnesia in the precipitate subsiding upon the ebullition of the water, and in the boiled water, is therefore dispensed with. However, if desirable, these substances may be determined according to the directions of 209. 2. In the analysis of a water so highly dilute that a preliminary con- centration is required, before the estimation of the chlorine and the sul- phuric acid can be effected, I recommend the following method : 1. ESTIMATION OF THE CHLORINE, PROTOXIDE OF IRON, PROTOXIDE OF MANGANESE, LIME, AND MAGNESIA. Transfer the water of several weighed bottles (together about 2000 grammes) to a porcelain dish ; rinse the bottles, and add the rinsings to the water in the dish. A precipitate of sesquioxide of iron may have formed in the bottles ; it is a matter of indifference whether the rinsing removes this completely or not. Evaporate the water to ^ ; pass the concen- trated fluid through a filter thoroughly washed with some nitric acid and water, and well wash the precipitate with boiling water. a. Acidify the JUtrate with nitric acid, precipitate with nitrate of silver, filter, and determine the chloride of silver in the usual way. Free the filtrate from the excess of silver by means of hydrochloric acid, evaporate, and then throw down, with oxalate of ammonia and phosphate of soda, the small quantity of magnesia which is never absent, and the minute traces of lime which may be present. (The precipitates are ignited and weighed with the principal quantities.) 6. Dissolve the precipitate, together with the residuary sediment which may still remain in the bottles, in hydrochloric acid, and treat the solution by one of the methods given iu 209, 4. 2. ESTIMATION OF THE SILICIC ACID, THE SULPHURIC ACID, AND THE ALKALIES. Evaporate the contents of several weighed bottles in a porcelain dish ; pour a little hydrochloric acid into the bottles, to dissolve the deposit of sesquioxide of iron, the hypothetical association of the acids and bases found in the water, it 13 assumed that the combination of these bases and acids is governed by their respective affinities, i. e., the strongest acid is assumed to be combined with the strongest base, <.;: 0-00737 Total . '. '-.,*. . . 0-09998 There remain ;'... * . . v 0-00855 of sulphuric acid, which combine with 0-00666 of soda, giving 0*01521 of SULPHATE OF SODA. . The rest of the soda present exists as chloride of sodium. Total amount of soda present . . . 0-54583 Combined with sulphuric acid . . 0-00666 There remain 0-53917 of soda, which correspond to 0-40123 of sodium, which latter, combining with 0-61040 of chlorine, give 1-01163 of CHLORIDE OF SODIUM. . The iodine and bromine are assumed to exist in combination with magnesium ; and the rest of the magnesium as chloride of mag- nesium. 510 ANALYSIS OF MINERAL WATERS. [ 213. 1. 0-000447 of iodine combine with 0*000044 of magnesium, giving 000491 Of IODIDE OF MAGNESIUM. 2. 0-000402 of bromine combine with 0-000065 of magnesium, giving 0-000467 of BROMIDE OF MAGNESIUM. Total amount of magnesium contained in the boiled water : 0-028855 Of which there are combined With iodine 0-000044 With bromine 0-000065 Total 0-000109 There remain . 0-028746 of magnesium, which are combined with 0-080220 of chlorine, givii 0-108966 Of CHLORIDE OF MAGNESIUM. c. Control. I. The joint amount of the lime in the boiled water and in the preci- pitate which forms upon ebullition must be equal or, at least, nearly so, to the total amount of the lime. Total amount of lime . *.. '. 0-10442 Combined with carbonic acid . ; . . 0-03642 Combined with sulphuric acid . . 0-06472 Total. .- ; -V . . . 0-10114 II. The amount of chlorine directly determined must correspond to the joint amount of the chlorine contained in the chlorides of sodium and magnesium. The joint amount of the chloride, bromide, and iodide of silver is . 2-807100 Subtract from this amount of iodide of silver corresponding to 0-000491 of iodide of magnesium, viz. . . 0-000828 And the amount of bromide of silver corresponding to 0-000467 of bromide of magnesium, viz. .... 0-000958 Total 0-001786 There remain ... . . 2'8053i4 which correspond to chlorine .... 0*69202 According to a . . . 0-61040 of chlorine are combined with sodium. And according to c . . 0-08022 of chlorine are combined with magnesium. Total". . . . . . 0-69062 III. The total amount of the fixed constituents must correspond to the joint amount of the several ingredients (the iron is here calculated asses- quioxide, since it is contained in that form in the residue). Total amount of the fixed constituents = 1 -37780 213.] ANALYSIS OF MINERAL WATERS. 511 The respective estimations of the several constituents Carbonate of lime . . 0-06533 magnesia . 0-00085 Sulphate of lime . . 0-15733 potassa . . 0-01602 soda . . 0-01521 Chloride of sodium . . 1-01163 magnesium . 0-10896 Iodide of magnesium . . 0-00049 Bromide of magnesium . 0-00047 Sesquioxide of iron . . 0-00066 Silica . : to.gaf ^ & . 0-00114 Total 1-37890* d. Arrangement and Classification of the Results. The analyst should state, in the first place, how many parts of the several constituents are contained in 100 or, better, in 1000 parts of the water ; and, in the second place, how many grains (1 Ib. = 7680 grs.) of the several constituents are contained in 1 pound of the water. The most appropriate way of classifying the results, is to enumerate them under the following heads : A. FIXED CONSTITUENTS. a. Present in ponderable quantity. b. Present in imponderable quantity. B. VOLATILE CONSTITUENTS. As regards the carbonates, it is a question whether they should be put down as neutral salts, the excess of carbonic acid being considered partly as forming bicarbonates, and partly as free acid ; or whether they should be calculated at once as bicarbonates, the excess of the carbonic acid being deemed to be present in the free state. Chemists sometimes adopt the one way, sometimes the other, but the former more frequently than the latter. I generally arrange the results of my analyses of mineral waters both ways, to facilitate comparison with the results of the analyses of similar springs. Besides stating the weight of the carbonic acid (and of the gases in general), it is customary to give also the volumes, calculated both in cubic centimetres and in cubic inches (1 Ib. of water = 32 cubic inches). These calculations are adjusted to the temperature of the spring. For similar examples to guide the young chemist in calculating and controlling the results of analyses of mineral waters, I refer to the fol- lowing papers, contained in my work on the analysis of the most im- portant mineral springs of the Duchy of Nassau, " Chemische Unter- * This control gives properly corresponding results only in the analysis of waters con- taining but small quantities of carbonate of magnesia, chloride of magnesium, and silicic acid, for the reasons stated 205, 7. In cases where these constituents are present iu large proportions, it is advisable to make, instead of or besides this control, a comparison of the sulphates (the iron being estimated as pure sesquioxide) with the residue obtained by evaporating the water with sulphuric acid and igniting ( 209, 1). 512 ANALYSIS OF MINERAL WATERS. [ 21-i. suchnngen der wichtigsten Mineral wasser des Herzogthums Nassau, von Professor Dr. R. Fresenius" published by Kreidel and Niedner, at Wiesbaden, from 1850 1857 ; also in " Jahrbiicher des nassauiscber naturhistorischen Vereins," vols. 6 12. 1. Analysis of the Eochbrunnen of Wiesbaden (hot saline springs). 2. Analysis of the mineral springs of Ems (thermal alkaline spring). 3. Analysis of the springs of Schlaugenbad (thermal springs holding only an extremely small quantity of solid constituents in solution). 4. Analysis of the mineral springs of Langenschwalbach (alkaline chalybeate springs, abounding in carbonic acid). 5. Analysis of the sulphuretted spring of Weilbach (cold hydrosul- phuretted spring), 6. Analysis of the mineral spring of Geilnau (alkaline chalybeate spring, abounding in carbonic acid). Papers 4, 5, and 6, have also been published in the " Journ. f. prakt. Chem.," vols. 64, 70, 72. Papers 1 and 2 contain also a detailed description of the methods em- ployed to determine the muddy ochreous and the solid sinter deposits of these springs. - II. ANALYSIS OF SOME OF THE MORE IMPORTANT TECHNICAL PRODUCTS AND MINERALS EMPLOYED IN THE ARTS, &c., WITH PROCESSES FOR ESTIMATING THEIR COMMERCIAL VALUE. 1. DETERMINATION OP THE AMOUNT OF ANHYDROUS ACID IN SOLUTION (ACIDIMETRY). A. ESTIMATION BY SPECIFIC GRAVITY. 214. THE specific gravity of an acid of course varies with the degree of its dilution. Tables, based upon the results of exact experiments, have been drawn up, expressing in numbers the relation between the specific gravity of the aqueous solution of an acid, and the amount of anhydrous acid contained in it. Therefore, to know the amount of anhydrous acid contained in an aqueous solution of an acid, it suffices, in many cases, simply to determine its specific gravity. Of course the acids must, in that case, be perfectly or at least nearly free from admix- tures of other substances dissolved in them. Now, as most acids are volatile (sulphuric acid, hydrochloric acid, nitric acid, acetic acid), any non-volatile admixture may be readily detected by evaporating a sample of the acid in a small platinum or porcelain dish. The determination of the specific gravity is effected either by com- paring the weight of equal volumes of water and acid ( 209), or by means of a good hydrometer. The results must, of course, be adjusted to the temperature to which the Tables refer. The following Tables give the relations between the specific gravity and the amount of anhydrous acid, for sulphuric acid, hydrochloric acid, nitric acid, and acetic acid. 214.] ACIDIMETRY. 513 Specific gravity of SULPHURIC ACID of different degrees of dilution, by Bineau ; calculated for 15 C. (59 F.), by Otto. Hydrated acid. Specific gravity. Anhydrous acid. Hydrated acid. Specific gravity. Anhydrous acid. 100 1-8426 81-63 50 1-398 40-81 99 1-842 80-81 49 1-3886 40-00 98 1-8406 80-00 48 1-379 39-18 97 1-840 79-18 47 1-370 38-36 96 8384 78-36 46 1-361 37-55 95 8376 77-55 45 1-351 36-73 94 8356 76-73 44 1-342 35-82 93 834 75-91 43 1-333 35-10 92 831 75-10 42 1-324 34-28 91 827 74-28 41 1-315 33-47 90 822 73-47 40 1-306 32-65 89 816 72-65 39 1-2976 31-83 88 809 71-83 38 1-289 31-02 87 1-802 71-02 37 1-281 30-20 86 1-794 70-10 36 1-272 29-38 85 1-786 69-38 35 1-264 28-57 84 1777 68-57 34 1-256 27-75 83 1767 6775 33 1-2476 26-94 82 1756 66-94 32 1-239 26-12 81 1745 66-12 31 1-231 25-30 80 1734 65-30 30 1-223 24-49 79 1722 64-48 29 1-215 23-67 78 1710 63-67 28 2066 22-85 77 1-698 62-85 27 198 22-03 76 1-686 62-04 26 190 21-22 75 1-675 61-22 25 182 20-40 74 1-663 60-40 24 174 19-58 73 1-651 59-59 23 167 18-77 72 1-639 58-77 22 159 17-95 71 1-637 5 7 -'95 21 1516 17-14 70 1-615 57-14 20 144 16-32 69 1-604 56-32 19 136 15-51 68 1-592 55-59 18 129 14-69 67 1-580 54-69 17 121 13-87 66 1-578 53-87 16 1-1136 13-06 65 557 53-05 15 1-106 12-24 64 545 52-24 14 1-098 11-42 63 534 51-42 13 1-091 10-61 62 '523 50-61 12 1-083 979 61 '512 49-79 11 1-0756 8-98 60 501 48-98 10 1-068 8-16 59 490 48-16 9 1-061 7-34 58 '480 47-34 8 1-0536 6-53 57 '469 46-53 7 1-0464 5-71 56 '4586 45-71 6 1-039 4-89 55 1'448 44-89 5 1-032 4-08 54 1-438 44-07 4 1-0256 3-26 53 1'428 43-26 3 1-019 2-445 52 1'418 42-45 2 1-013 1-63 51 1-408 41-63 1 1-0064 0-816 II. 514 ACIDIMETEY. [ 214. Specific gravity of dilute HYDROCHLORIC ACID containing different proportions of hydrochloric acid gas, by Ure. Temperature 15 C. (59 E.) Specific gravity. Hydrochloric acid gas. Specific gravity. Hydrochloric acid gas. 1-2000 40-777 1-1000 20-388 1-1982 40-369 1-0980 19-980 1-1964 39-961 1-0960 19-572 1-1946 39-554 1-0939 19-165 1-1928 39-146 1-0919 18-757 1-1910 38-738 1-0899 18-349 1-1893 38-330 1-0879 17-941 1-1875 37-923 1-0859 17-534 1-1857 37-516 1-0838 17-126 1-1846 37-108 1-0818 16718 1-1822 36-700 1-0798 16-310 1-1802 36-292 1-0778 15-902 1-1782 35-884 1-0758 15-494 1-1762 35-476 1-0738 15-087 1-1741 35-068 1-0718 14-679 1-1721 34-660 1-0697 14-271 1-1701 34-252 1-0677 13-863 1-1681 33-845 1-0657 13-456 1-1661 33-437 1-0637 13-049 1-1641 33-029 1-0617 12-641 1-1620 32-621 1-0597 12-233 1-1599 32-213 1-0577 11-825 1-1578 31-805 1-0557 11-418 1-1557 31 -398 1-0537 11-010 1-1537 30-990 1-0517 10-602 1-1515 30-582 1-0497 10-194 1-1494 30-174 1-0477 9-786 1-1473 29-767 1-0457 9-379 1-1452 29-359 1-0437 8-971 1-1431 28-951 1-0417 8-563 1-1410 28-544 1-0397 8-155 1-1389 28-136 1-0377 7-747 1-1369 27-728 1-0357 7-340 1-1349 27-321 1-0337 6-932 1-1328 26-913 1-0318 6-524 1-1308 26-505 1-0298 6-116 1-1287 26-098 1-0279 5-709 1-1267 25-690 1-0259 5-301 1-1247 25-282 1-0239 4-893 1-1226 24-874 1-0220 4-486 1-1206 24-466 1-0200 4-078 1-1185 24-058 1-0180 3-670 1-1164 23-650 1-0160 3-262 1-1143 23-242 1-0140 2-854 1-1123 22-834 1-0120 2-447 1-1102 22-426 1-0100 2-039 1-1082 22-019 1-0080 1-631 1-1061 21-611 1-0060 1-124 1-1041 21-203 1-0040 0-816 1-1020 20-796 1-0020 0-408 214.] ACIDIMETRY. 515 TABLE III. Specific gravity of dilute NITRIC ACID containing different proportions of anhydrous acid, by Ure. Temperature 15 C. (59 F.) Specific gravity. Per-cents of acid. Specific gravity. Per-cents of acid. Specific gravity. Per-cents of acid. Specific gravity. Per-cents of acid. 1-500 79-7 419 59-8 1-295 39-8 1-140 19-9 1-498 78-9 415 59-0 1-289 39-0 1-134 19-1 1-496 78-1 411 58-2 1-283 38'3 1-129 18-3 1-494 77-3 406 57-4 1-276 37-5 1-123 17'5 1-491 76-5 402 56-6 1-270 367 1-117 16-7 1-488 75-7 398 55-8 1-264 35-9 1-111 15-9 485 74-9 394 55-0 1-258 351 1-105 15-1 482 74-1 1-388 54-2 1-252 34-3 1-099 14-3 479 73-3 1-383 53-4 1-246 33-5 1-093 13-5 476 72-5 1-378 52-6 1-240 32-7 1-088 12-7 473 717 1-373 51-8 234 31-9 1-082 11-9 470 70-9 1-368 51-1 228 31-1 1-076 11-2 467 70-1 1-363 50-2 221 30-3 1-071 10-4 464 69-3 1-358 49-4 215 29-5 1-065 9-6 460 68-5 1-353 . 48-6 208 287 1-059 8-8 457 677 1-348 47-9 202 27-9 1-054 8-0 453 66-9 1-343 47-0 196 27-1 1-048 7-2 1-450 66-1 1-338 46-2 189 26-3 1-043 6-4 1-446 65-3 1-332 45-4 183 25-5 1-037 5-6 1-442 64-5 1-327 44-6 177 247 1-032 4-8 1-439 63-8 1-322 43-8 171 23-9 1-027 4-0 1-435 63-0 1-316 43-0 165 23-1 1-021 3-2 1-431 62-2 1-311 42-2 159 22-3 1-016 2-4 1-427 61-4 1-306 41-4 153 21-5 1-011 1-6 1-423 60-6 1-300 40-4 146 207 1-005 0-8 TABLE IV. Specific gravity of dilute ACETIC ACID containing different proportions of hydrated acid, by Molir. Per Specific cents. 1 gravity. Per cents. Specific gravity. Per cents. Specific gravity. Per cents. Specific gravity. Per cents. Specific gravity. 100 1-0635 80 1-0735 60 1-067 40 1-051 20 1-027 99 1-0655 79 1-0735 59 1-066 39 1-050 19 1-026 98 1-0670 78 1-0732 58 1-066 38 1-049 18 1-025 97 1-0680 77 1-0732 57 1-065 37 1-048 17 1-024 96 1-0690 76 1-0730 56 1-064 36 1-047 16 1-023 95 1-0700 75 1-0720 55 1-064 35 1-046 15 1-022 94 1-0706 74 1-0720 54 1-063 34 1-045 14 1-020 93 1-0708 73 1-0720 53 1-063 33 1-044 13 1-018 92 1-0716 72 1-0710 52 1-062 32 1-042 12 1-017 91 1-0721 71 1-0710 51 1-061 31 1-041 11 1-016 90 1-0730 70 1-0700 50 1-060 30 1-040 10 1-015 89 1-0730 69 1-0700 49 1-059 29 1-039 9 1-013 88 1-0730 68 1-0700 48 1-058 28 1-038 8 1-012 87 1-0730 67 1-0690 47 1-056 27 1-036 7 1-010 86 1-0730 66 1-0690 46 1-055 26 1-035 6 1-008 85 1-0730 65 1-0680 45 1-055 25 1-034 5 1-007 84 1-0730 64 1-0680 44 1-054 24 1-033 4 1-005 83 1-0730 63 1-0680 43 1-053 23 1-032 3 1-004 82 1-0730 62 1-0670 42 1 -052 22 1-031 2 1-002 81 1-0732 61 1-0670 41 1-051 21 1-029 1 1-001 L L 2 516 ACTDIMETRY. [ 215. In all cases in which the determination of the specific gravity fails to attain the end in view, or which demand particular accuracy, one of the two following methods is employed, but more commonly the first. B. DETERMINATION OF THE ANHYDROUS ACID BY SATURATION WITH AN ALKALINE FLUID OP KNOWN STRENGTH.* 215. This method requires : a. A dilute acid of known strength. /J. An alkaline fluid also of known strength. aa. Preparation of the Solutions. a. The dilute acid must contain in 1000 c.c. the exact equivalent number of the acid (H=l) in grammes, accordingly, 40 grammes of sulphuric acid, 36'46 of hydrochloric acid, 36 of oxalic acid, drc. Acids of this degree of dilution are called normal or standard acids ; equal volumes of them severally neutralize eqiial quantities of alkalies. The normal or standard sulphuric acid is generally used ; or the normal or standard oxalic acid, as recommended by Mohr, may be employed. Preparation of Standard Sulphuric Acid' Mix, in a large flask, 1020 cubic centimetres of water intimately with 60 grammes of concentrated sulphuric acid ; allow the mixture to cool, take two portions of it of 20 c.c. each, and detei-mine the amount of sulphuric acid in them by precipitation with chloride of barium ( 132, I., 1). If the two experiments agree pretty nearly, take the mean of the results as the amount of sulphuric acid contained in the solution, an'l dilute the latter with the necessary quantity of water to give a fluid containing in 1000 c.c. exactly 40 grammes of anhydrous sulphuric acid. Suppose that 1000 c.c. of the solution contain 42 grammes of sulphuric acid, then, according to the proportion, 40 : 1000:: 42 :x; s=1050, you will have to add 50 c.c. of water to 1000 c.c. of the solution. This may be effected most simply and accurately in the following manner : Fill a measuring flask holding 1 litre, up to the litre mark with the dilute acid, and pour the latter from this flask cautiously into a larger bottle ; measure in a pipette 50 c.c. of water, transfer to the measuring flask which contained the acid, shake the water well about in the flask, and then add it to the solution in the larger bottle. Shake the mixture well, pour back about half into the measuring flask, shake about in the latter, and then transfer again to the large bottle. Shake, and keep for use. As the fluid only half fills the larger bottle, water will after a time evaporate, which will condense on the sides in the upper part of the vessel ; it is necessary, therefore, to shake the bottle each time before using its contents ; otherwise the portion poured out first will contain more water, and accordingly less acid, than the remaining fluid. * According to Nicholson and Price (" Chem. Gaz.," 1856, p. 30) the common n ' acitlimetry is not suited for determining free acetic acid, on account of the alkali method of acidi action of neutral acetateof soda ; however, Otto (" Annal. d. Chem. u. Pharm.," 102, 69) has clearly demonstrated that the error arising from this is so inconsiderable that it may safely be disregarded. 215.] ACIDIMETKY. 517 Preparation of Standard Oxalic A cid. Introduce 1 equivalent, i.e., 63 grammes, of pure crystallized oxalic acid (C O S , H O + 2 Aq), accurately weighed, into a litre flask, add water at 60 F., dissolve by shaking, dilute up to the litre mark with water at 60 F., shake, and keep for use. The solution muht be shaken each time previous to using it, for the same reason as the sulphuric acid solu- tion. Care must be taken to employ perfectly pure oxalic acid, abso- lutely free from moisture, and without the least sign of efflorescence. /3. For alkaline solution a solution of soda is used, of which 1 volume exactly neutralizes 1 volume of standard acid ; the point of neutralization being indicated by the blue coloration imparted by the last drop of solu- tion of soda added to the acid solution slightly reddened by litmus. An alkaline solution of this strength is called normal or standard solu- tion of soda. 1000 c.c. of it saturate 1 equivalent of each acid (H= 1), expressed in grammes. To effect this, dilute a fresh prepared, perfectly clear solution of soda, quite free from carbonic acid, to a specific gravity of about 1*05, which corresponds to about 3-6 per cent, of soda. Measure off 50 c.c. of the standard acid, transfer to a beaker, impart a faint red tint to the fluid by means of tincture of litmus,* and let the standard solution of soda flow into the reddened fluid, from a burette with compression-clamp, until the mixture just shows a blue tint, and consequently leaves both red and blue litmus paper unaltered. Dilute now the still somewhat too con- centrated solution of soda with the requisite quantity of water to give a fluid of which exactly 50 c.c. are required to saturate 50 c.c. of the standard acid. Suppose, therefore, you have used 47 c.c. of the solution of soda, you will have to add 3 c.c. of water to every 47 c.c. of the solu- tion, and accordingly 63*83 c.c. of water to 1 litre. The best way of effecting this dilution has already been described in a. Close the flask in which the dilute solution of soda is kept, with a cork into which is fitted a small bulb tube of the form of a chloride of calcium tube, filled with a finely triturated mixture of sulphate of soda and caustic lime, and bearing a thin open tube in the exit aperture (Mokr). Besides this solution of soda, prepare another, 5 times more dilute, and a third, 10 times more dilute. This is effected best for instance, as regards the latter fluid by measuring in a pipette 50 c.c. of the more concen- trated solution of soda, transferring the fluid to a measuring flask hold- ing exactly 500 c.c., then filling the flask with water, exactly up to the mark, and mixing intimately by shaking. bb. The Volumetrical Process. As 1000 c.c. of the standard solution of soda correspond to 1 equiva- lent, 1000 c.c. of the 5 times more dilute solution to ^, and 1000 c.c. of the decimal solution to T \j- equivalent of each acid expressed in grammes, there is hardly anything further to be said about the process, the selection of either of the three alkaline fluids depending, of course, en- tirely upon the quantity of acid to be neutralized. The neutralization of the weighed or measured acid fluid should take about 15 30 c.c. * As the tincture of litmus is often so alkaline that a notable amount of acid is required to redden it, the excess of alkali must, if necessary, be neutralized ; the tincture so prepared gives upon dilution with water a violet-colored fluid, to which a trace of acid imparts a red, aud the least quantity of alkali a blue tint ( 65, 2). 518 ACIDIMETRY. [ 215. In scientific investigations, I recommend the weighing of indetermi- nate quantities of the acid fluid, as this may be done with comparative ease on a chemical balance, and the trifling trouble of calculation is not worth mentioning. Suppose, for instance, you have weighed off 4*5 grms. of dilute acetic acid, and used 25 c.c of standard solution of soda to neutralize this, you find by the proportion, 1000 : 60 (equivalent of C 4 H 4 OJ :: 25 : x a;=l-5, that 1'5 grms. of hydrated acetic acid are contained in the weighed quantity of the dilute acid ; and another proportion, viz., 4-5 :l-5::100:aj; x = 33-33, gives the per-centage amount of hydrated acetic acid contained in the analysed fluid. Or, the calculation may also be made as follows : 4 '5 grms. of the acetic acid examined having required 25 c.c. of standard solution of soda for neutralization, how much would 6 grammes (i.e. the weight of -j^ equivalent of hydrated acetic acid) require ? 4-5 :25::6 :x; *= 33-33 It is evident that in this case the number of cubic centimetres found as x, expresses the per-centage amount of hydrated acetic acid contained in the examined fluid, since 100 c.c. of standard solution of soda cor- respond to T ^ equivalent of pure hydrated acetic acid, i.e. acetic acid of 100 per cent. In technical analyses it is more convenient if the number of c.c., or half c.c. used of the standard solution of soda expresses directly, and without need of further calculation, the per-centage amount of hydrated or anhydrous acid contained in the examined fluid. For this purpose, the iV or irtr equivalents (H = I) of the anhydrous or hydrated acid, ex- pressed in grammes, are weighed off the T \f equivalents if the number of c.c., the 2Tj- equivalents if the number of half c.c. used of standard solution of soda, are to express the per-centage amount of hydrated or anhydrous acid contained in the analysed fluid. The following are the quantities for the more common acids : T \y Equivalent %$ Equivalent in grammes. in grammes. Sulphuric acid . . .4-0 . . .2-00 Hydrated sulphuric acid . 4-9 " -..-. ': .-* . 2-45 Nitric acid . . . .5*4 ...>-. . 2-70 Hydrated nitric acid . .6*3 . . .3-15 Hydrochloric acid . . . 3'646 . . . 1-823 Oxalic acid . . . .36 . . . 1 -80 Crystallized oxalic acid . .6-3 . . .3-15 Acetic acid .... 5-1 ... 2-55 Hydrated acetic acid . .6*0 . . .3-00 Tartaric acid . . . .6-6 . . .3-30 Hydrated tartaric acid . .7-5 . .3-75 But, as the weighing of definite small quantities is less accurate, it is preferable to weigh off the half equivalents of the acids (i.e. 20 or 24 - 5 grammes of sulphuric acid, according to whether it is intended to find the per-centage amount of anhydrous or of hydrated acid ; 18'23 of hydrochloric acid, until the formation of water ceases. The loss of weight expresses the quantity of oxygen in the sesquioxide, from which the amount of the latter may be calculated. c. Treat the residue with dilute hydrochloric acid. The iron dissolves, the admixture from the matrix is left. Filter, heat the nitrate, which generally already contains some sesquichloride of iron, with a fragment of zinc ( 1 13, b, 2, a), best in a current of hydrogen gas ( 149, II., a, a), until complete reduction is effected, and determine the iron finally by solution of permanganate of potassa ( 112, b, 2, a). The result must agree with that of b ; if the results of the two processes differ, that of c may generally be considered the more reliable of the two. d. Dry, heat, ignite, and weigh the residue obtained in c, which con- tains the titanic acid if any is present. To detect and determine it, 239.] ANALYSIS OF IRON ORES. 557 boil the residue, in a platinum crucible, with concentrated sulphuric acid, mixed with a little water. .When the greater portion of the sulphuric acid has evaporated, dilute the residue largely with water, filter, and separate the titanic acid by long-continued boiling ( 107). e. The water may be determined by igniting a separate portion of the powder. If the ore contains carbonates of the alkaline earths, the car- bonic acid of the latter escapes with the water. II. BROWN HEMATITE. This ore contains the iron, or the far greater part of it, as hydrated sesquioxide, and, besides, alumina and sesquioxide of manganese: often also small quantities of lime and magnesia, and of silicic acid (in combi- nation with bases), phosphoric acid, and sulphuric acid, and always a larger or smaller admixture of quartz saud or gangue* insoluble in hydrochloric acid. A complete and accurate analysis of this ore presents some difficulties. One of the following methods may be selected. The preliminary opera- tions indispensable in all of them are the reduction of the ore to a fine powder, which is dried at 212 F., or under the exsiccator, and the igni- tion of a sample, to ascertain the amount of water. In the latter process, it must be borne in mind that, in presence of carbonates of the alkaline earths, or carbonate of protoxide of iron, the water must not be estimated from the loss of weight, but determined by direct weighing ( 36). a. Decomposition in the Dry Way. (This method is more particularly recommended for the analysis of ores containing only small quantities of silicic acid, alumina, lime, and magnesia.) Fuse a weighed portion of the powder with three times its weight of carbonate of soda and potassa, and boil the fused mass with water until the soluble parts are dissolved ; filter the solution from the residue, and well wash the latter. aa. The filtrate contains, besides the excess of carbonate of soda, the soda salts of the acids present in the analysed ore (silicic acid, phos- phoric acid, sulphuric acid, and, perhaps, also arsenic acid, chlorine, and fluorine) ; generally, however, the first three acids alone are present in an appreciable proportion. Acidify the alkaline filtrate with hydrochloric acid and separate the silicic acid in the usual way ( 140, II., a). Add to the filtrate a few drops of chloride of barium, allow to stand for 24 hours, and then filter off the precipitate of sulphate of baryta which may have formed. Remove the baryta from the filtrate by means of a few drops of dilute sulphuric acid, and then precipitate the phosphoric acid with magnesia, as directed 134, I., b. Should arsenic acid be present, this must be removed by sulphu- retted hydrogen, before the precipitation of the phosphoric acid. bb. Dissolve the residue in hydrochloric acid, separate the silicic acid, which is generally present in this solution, as directed 140, II., a, and treat the filtrate with sulphuretted hydrogen, to precipitate any traces of copper that might be present ; then separate the iron, manganese, alumina, lime, and magnesia, by one of the methods given in 161. * Besides these substances, which are generally found in brown hematite, traces of other bodies are often also detected by a searching analysis. Thus A. Miiller (" Annal. d. Chein. u. Pharrn .," 86, 127) found in a variety of pea-iron ore (Carlshiitte, near Alfeld) ponderable traces of potassa, arsenic acid, and vanadic acid, and imponderable traces of chromium, copper, and molybdenum. 558 ANALYSIS OF IKON ORES. [ 239. b. Decomposition in the Humid Way. Heat about 10 grammes of the finely pulverized mineral, in an ob- liquely placed flask, with concentrated hydrochloric acid, until complete decomposition is effected ; evaporate on the water-bath to dryness, moisten the residue with hydrochloric acid, heat gently, dilute with water, filter into a measuring flask holding 250 c.c., and wash ; dry, ignite and weigh the undissolved residue ; it consists of quartz sand or gaugue, and liberated silicic acid. The latter may be separated and determined, by boiling the residue with a solution of carbonate of soda ( 235, 6). The filtrate is diluted to the volume of 250 c.c., and then treated as follows : 1. To determine the sulphuric acid, evaporate 50 c.c. until the greater part of the hydrochloric acid is removed, then dilute with about 200 c.c. of water, add chloride of barium, and let the mixture stand at least 24 hours ; then filter off the trifling precipitate of sulphate of baryta which generally forms. 2. Determine, in another portion of 50 c.c., the phosphoric acid, by means of molybdate of ammonia ( 134, I., 6, ft*). If arsenic acid is present, this must first be removed by sulphuretted hydrogen ( 1 66, 1), as molybdic acid precipitates this acid also. 3. In another portion of 50 c.c., determine the iron volumetrically, by solution of permanganate of potassa, after previous reduction of the sesquioxide by boiling with zinc ( 113, 6, 2, a). 4. Treat another portion of 50 c.c. as directed 161,2 (96), to deter- mine the iron once more, and also the manganese, alumina, and alkaline earths. As phosphoric acid (and arsenic acid, if present) pass into the precipitate produced by acetate of soda, regard must be had to the pos- sible presence of these acids, in estimating the alumina -by the difference. If the qualitative analysis has given ponderable traces of copper or arsenic acid, these substances must first be removed by sulphuretted hydrogen ; in which case the reduced protoxide of iron is again peroxi- dized by nitric acid, before proceeding as above directed. III. BOG IRON OBE. Bog iron ore consists of a mixture of hydrated eesquioxide of iron with the basic salts of sesquioxide of iron with silicic acid, sulphuric acid, phosphoric acid, arsenic acid, crenic acid, apocrenic acid, and humic acid, and generally contains besides these, gangue, alumina, lime, and magnesia. Eeduce the ore to powder, and dry. Expose a portion of it, in an open platinum crucible, at first to a dull red heat, to burn the organic acids, then gradually for some time to an intense red heat, with the crucible placed in an oblique position. The loss expresses the amount of water and organic substances originally present in the ignited ore. Treat another sample by one of the methods given in II. ; the sample may previously be very gently ignited, only j ust sufficient to destroy the organic substances. To detect and determine the organic acids, boil a larger portion of the finely pulverized ore with pure solution of j.otassa, until it is converted into a flocculent mass. Filter and treat the filtrate as directed 209, 10. * The method described $ 135, i., 7, may also be resorted to. 210.] ANALYSIS OP IRON ORES. 559 IV. MAGNETIC IRON ORE. Magnetic iron ore contains the metal as protosesquioxide. Analyse the ore in the same way as the red hematite, and determine afterwards in a sepai*ate weighed poi'tion, dissolved in hydrochloric acid, in a current of carbonic acid, the protoxide of iron by volumetric analysis, as directed 112,6, 2, a. V. SPATHIC IRON ORE. Spathic iron ore contains carbonate of protoxide of iron, associated usually with carbonate of manganese and carbonates of the alkaline earths, and often mixed also with clay and gangue. Reduce the mineral to powder and dry. a. Determine the water as directed 36. b. Determine the carbonic acid as directed 139, II., e, a or /3. c. Dissolve a third portion of the powder in hydrochloric acid, with addition of nitric acid. When complete decomposition has been effected, filter the fluid from the undissolved residue, and separate the bases in the filtrate as directed in II., 6, 4, or by one of the methods given in 161. d. In a fourth portion of the powder, dissolved in hydrochloric acid, in a current of carbonic acid, determine the quantity of the protoxide of iron volumetrically, as directed 1 12, b, 2, a. e. If the residue insoluble in hydrochloric acid is considerable, proceed with it as directed 235 (Analyis of Silicates). B. ESTIMATION OP THE IRON IN IRON ORES. 240. This is now almost exclusively effected by means of solution of perman- ganate of potassa. Heat 0-5 grm. of the finely pulverized ore, dried in the air; or at 212 F., in a long-necked flask, placed obliquely, witU concentrated hydrochloric acid until complete decomposition is effected ; dilute with about 30 c.c. of water, reduce with zinc, and proceed exactly as directed 113, 6, 2, a. 2. In the supplement to 112 and 113, Fuchss indirect method of estimating iron ("Journ. f. prakt. Chem.," 17, 160) is stated to give neither accurate nor constant results. However, it would now appear, from two recent papers on the subject, one by J. Lowe (" Journ. f. prakt. Chem.," 72, 28), the other by R. Jtonig ("Journ. f. prakt. Chem.," 72, 36), that this unfavourable opinion was based upon erroneous data, and that the method, which I will now proceed to describe, is very suitable for technical purposes. a. Common method (as described by Lowe, " Journ. f. prakt. Chem.," 72, 28). If the ore intended for analysis is of a superior kind, take 1 1-5 grin., if an inferior ore, 2 3 grammes ; reduce to very fine powder, and heat, in an obliquely placed long-necked glass flask of about 500 c.c. capacity, with strong hydrochloric acid ; when all sesquioxide of iron is dissolved, add, gradually, small pieces of fused chlorate of potasaa. until the fluid smells distinctly of chlorine, and continue heating until this smell is no longer perceptible. Dilute with water until the flask is half fall, and then insert a sound cork, in which a glass tube, open at 560 ANALYSIS OF IRON ORES. [ 240. both ends, about 10 inches long, and not too narrow, is fitted air-tight : place the flask in a slanting position, and heat for, at least, 15 minutes to moderate boiling, to ensure the expulsion of every trace of chlorine and atmospheric air. Whilst keeping the solution in incessant ebullition, open the cork, and suspend in the neck of the flask a strip of pure clean sheet copper, at- tached to a platinum wire, inserting the cork again so as to keep the wire in position ; when the copper strip has become sufficiently hot to allow of its immersion in the fluid, without danger of spurting, open the cork again, let down the strip of copper horizontally to the bottom of the flask, so as to immerse it completely in the fluid; insert the cork now firmly, place the flask again in a slanting position, taking care to keep the fluid during this manipulation in incessant, though slow and moderate ebullition, and continue this until the iron in the solution is com- pletely reduced, and appeal's, accordingly, quite colorless, or at least exhibits but a very inconsiderable and indistinct greenish tint. The object of the process is generally attained in about 2 hours, but the boil- ing may be continued for 3 or 4 hours without the least detriment to the accuracy of the results. The strip of copper must always remain completely covered by the fluid ; it is for this reason that so large a quantity of water is* added at first, as any subsequent additions would of course be quite impracticable. The strip of copper should weigh about 6 grammes, it should be made of copper precipitated by galvanic action, and of the proper breadth and length to pass readily through the neck of the flask and lie at the bottom in a horizontal position. It is scoured clean with sand paper, weighed, and then attached to the platinum wire. When the reduction of the iron is completed, uncork the flask, promptly withdraw from the still boiling fluid the strip of copper, by means of the platinum wire ; immerse in a beaker filled with distilled water, take out again, rinse by means of the washing bottle, dry completely between blotting paper, take off the platinum wire, weigh, and reckon for each equivalent of copper dissolved in the process, as indicated by the loss of weight of the strip, 1 equivalent of iron (see Supplement to 112 and 113, a). The copper is found to have lost its original lustre in the pro- cess, and looks dull, but not blackish, as is generally the case if ordinary sheet copper is used. In four analyses of chemically pure sesquioxide of iron, J. Lowe obtained by this process, severally, 99'7, 99 6, 99'6, 99'6 per cent, of sesquioxide of iron. Konig's process ("Journ. f. prakt. Chem.," 72, 36) is nearly the same as Lowes. He recommends, however, to keep the strip of copper, after its removal from the boiling fluid, for some time in hot water, to ensure the removal of every particle of the solution which may have penetrated into the pores of the metal ; then to remove the water by immersion in absolute alcohol, and the latter again by immersion in ether. He also recommends to wind platinum wire round the strip, which, besides accelerating the reduction, will prevent the scaling off of small particles of the copper, that might otherwise be caused by the bumping of the metal against the sides of the vessel during the process of ebullition. The results which Konig's obtained by this process, in a series of experiments, varied between 99 '5 and 100-5 per cent. 6. Modified Process. If the ore contains an appreciable proportion of titanic acid, Fuclis" 241, 242.] ANALYSIS OF COPPER PYRITES AND GALENA. 561 process (a) reqiiires certain modifications, for which I i-efer to the ori- ginal paper on the subject (" Journ. f. Prakt. Chem.," 18, 495 ; see also Konig, " Journ. f. Prakt. Chem.," 72, 58), as cases of the kind are of com- paratively rare occurrence. If the ore contains arsenic acid, the process is inapplicable, as a coating of blackish scales of arsenide of copper would form on the copper. The arsenic acid may be removed, however, by fusing the pulverized ore with carbonate of soda, and extracting the fused mass with water, dissolving the residue in hydrochloric acid, and treat- ing the solution as in a. 12. COPPER PYRITES. 241. This mineral contains copper, iron, sulphur, and generally also ganguc. Whether it contains other metals, besides copper and iron, must be as- r certained by a qualitative analysis. The finely pulverized mineral is dried at 212 F. a. The estimation of the sulphur is generally effected in the humid way, according to the directions given 148, II., 2, a; but it may be effected also as directed 148, II., 2, b, or in the dry way ( 148, II., 1). b. If nitric acid is used as oxidizing agent ( 148, II., 2, a) the bases art, 1 either determined in a fresh sample of the mineral, or the excess of baiyta is removed by sulphuric acid, the fluid evaporated, to expel the nitric acid as completely as possible, and the copper and iron are then finally separated by means of sulphuretted hydrogen ( 162, A), or by hyposul- phite of soda ( 162, B, 4, a, 112). But if the sulphur is estimated by fusion with nitrate of potassa and carbonate of soda ( 148, II., 1), or the mineral in alkaline solution is decomposed by chlorine ( 148, II., 2, 6), the residual oxides of iron and copper are dissolved in hydrochloric acid, and then separated by one ol the processes described. Which of these methods should be preferred, depends upon the presence of appreciable quantities of other metals besides copper and iron ; if zinc blende is present, the first method is preferable ; if arsenic, one of the two latter methods. In complicated cases, treatment with chlorine in the dry way is resorted to ( 148, II., 1, c). If the quantity of copper alone is to be determined, and no other metal precipitable by zinc is present, the mineral may be decomposed with hydrochloric acid and chlorate of potassa, the solution evaporated to dryness, the residue dissolved by hydrochloric acid and water, the solution filtered into a platinum dish, and the copper precipitated by zinc ( 119, 2). Or Schwarzs volumetric method ( 119, 4, a) may bt employed ; but, in effecting the reduction, care must be taken not tc raise the heat above 176 F., at which temperature iron will not precipitate from a fluid containing a large proportion of alkaline tartrate. However, even supposing some iron to precipitate with the copper, this could exercise no adverse influence on the quantitative estimation of the latter metal. 13. GALENA. 242. Galena, the most widely spread of the lead ores, frequently contains larger or smaller quantities of iron, copper, silver, and commonly also gavigue, more or less insoluble in acids. n. o o 562 ANALYSIS OF SILVER IX GALEXA. [ 243. The best way of analysing it, is as follows : Reduce the ore to a tine powder, and dry at 212 F. Oxidize a weighed quantity of the powder (1 2 grammes) with highly concentrated red fuming nitric acid, free from sulphuric acid (see 1 48, II., 2, a, a ; however, the ore is not exposed in a tube to the action of the acid). If the acid is sufficiently strong, the whole of the sulphur is oxidized. After heating gently for some time, dilute with, water, filter, and wash the residue. a. Dry the residue, ignite, and weigh ( 116, 2). It consists of sul- phate of lead, gangue uudecomposed by the acid, silicic acid, 3 (18) ; determine the alkalies as chlorides, and separate them, if required, according to the directions of 152. If the solution contains an appreciable quantity of manganese, precipitate this first, after the removal of the phosphoric acid, with sulphide of ammonium. Mix b with ammonia in slight excess, then add acetic acid until the precipitated phosphates of the alkaline earths are redissolved. Filter the phosphate of sesquioxide of iron, which remains undissolved, and treat as in 252, 2, a. Divide the filtrate into two equal parts, a and /3, and determine in a the pliosphoric add as phosphate of sesquioxide of uranium, as directed 134, c; in j3 the lime and magnesia as directed 154, 4, b (31). If the ash contains an appreciable quantity of manganese, the latter must be removed from the portion intended for the estimation of the lime and magnesia (/3), as that metal will otherwise precipitate partly with the lime, partly with the magnesia. In that case, therefore, heat (3 (which still contains alkaline acetate, the fluid having been mixed with acetic acid) to 122 140 F., and transmit chlorine through it ( 159, B, 4, a, f3 [58])- The fluid b may also be treated as follows : Proceed first as above directed ; after the separation of the phosphate of sesquioxide of iron, precipitate the lime from the acetic acid solution by oxalate of ammonia ( 103, 2, b, ft). Filter, divide the filtrate into two equal parts, and determine the magnesia in one, by addition of ammonia and phosphate of soda ; the phosphoric acid in the other, by addition of ammonia and solution of sulphate of magnesia mixed with chloride of ammonium. In presence of an appreciable quantity of manganese, this latter method gives less satisfactory results. If the phosphoric acid is present in the 592 ANALYSIS OF THE ASHES OF PLANTS. [ 254, 255. ash in form of bibasic salts, the safest way is to evaporate the portion intended for the estimation of the phosphoric acid, finally in a platinum dish, fuse the residue with carbonate of soda, dissolve the fused mass in water, and determine the phosphoric acid in the solution either as phos- phate of sesquioxide of uranium, or by addition of ammonia and solution of sulphate of magnesia mixed with chloride of ammonium. III. AsJies not decomposed by Hydrochloric Acid. 254. The carbonic acid, which, however, is rarely found in ashes of this class, is determined according to the directions of 252. The same applies to chlorine. The estimation of the other constituents requires a preliminary decomposition of the ash ; this may be effected in several ways, as follows : 1. Evaporate the ash with pure solution of soda to dryness, in a plati- num or silver dish. (The results of many experiments have shown that by this operation the silicates in the ash are completely decomposed, whilst the sand which may be mixed with the ash is left untouched, or, at least, nearly so. The heat must not be raised in the last stage of the process sufficiently high to fuse the mass.) Pour dilute hydrochloric acid over the residue, evaporate, treat again with hydrochloric acid, and proceed with the insoluble residue (silica, charcoal, and sand), as directed in 252, A, 1 ; with the solution as directed in 252, A, 2, or 3. The alkalies cannot, of course, be determined in the solution ; they are esti- mated in a separate portion of the ash, which for this purpose is decom- posed either by hydrofluoric acid, or by fusion with hydrate of baryta (Fresenius and Will). 2. Way and Ogston * mix the ash with an equal weight of nitrate of baryta, and fuse the mixture gradually in a large platinum crucible (transferring it to the crucible in small portions at a time). By this process the ash is fully prepared for decomposition by hydrochloric acid, and the charcoal which it may contain is completely destroyed, leaving the ash perfectly white. The silicic acid is separated according to the direction given in 252, A, 1, and the sulphate of baryta which may be present determined. Of the hydrochloric acid solution, Way and Ogston use a portion for the estimation of the alkalies, by the method described in 252, A, 2, c. ; they precipitate the remainder with sulphuric acid, added slightly in excess ;f they then divide the filtrate into two portions, and determine in one the phosphate of sesquioxide of iron, the lime and magnesia ( 253) ; in the other the phosphoric acid, as directed 134, 4* C. CALCULATION AND ARRANGEMENT OF THE RESULTS. 255. It is only recently that chemists have begun to turn their attention seriously to the analysis of the ashes of plants, for the benefit of vegetable *" Journal of the Royal Agricultural Society," VIII., Part 1; LieUg and Kopp's "Annual Report," 1849, 600. t As the quantity of nitrate of baryta used is known, an excess over the calculated weight of sulphate of baryta shows that lime has been thrown down with the baryta : the quantity of this sulphate of lime is calculated from the excess of the weight of the precipitate. 255.] ANALYSIS OF THE ASHES OF PLANTS. 593 physiology and agriculture. The questions which it is intended to solve by the analysis of the ashes of plants, are principally the following : 1. Do plants absolutely require certain quantities of certain consti- tuents 1 and if so, wJiat are these constituents ? 2. May some of these inorganic constituents be replaced by others ? It is quite obvious that a proper and perfectly satisfactory solution of these questions can be expected only from the results of an exceedingly large number of analyses, and that a great many chemists must contribute towards such a solution. Under these circumstances, it is of the utmost importance that the results of all analyses of vegetable ashes should be invariably arranged and reported in a uniform manner, so that they may be compared readily and without recalculation. As the manner in which the bases and acids found were originally combined iu the plant cannot be inferred from the ash with any degree of certainty, and since, moreover, as I have already had occasion to state, the ashes differ as regards the phosphates, &c., according to the degree of heat employed, it is unquestionably the most judicious way to enu- merate ^.he per-centage weights of the bases and acids separately. The chlorine, however, is put down as chloride of sodium, and, should the quantity of soda present be insufficient, as chloride of potassium, the proportion of sodium contained in the chloride is calculated as soda, and the calculated weight subtracted from the total amount of soda found ; since, otherwise, a surplus would be invariably obtained in the analysis, as the chloride of sodium originally present in the ash would be reckoned as chlorine and soda, instead of chlorine and sodium. The manganese which may be present is entered as proto-sesquioxide, since it exists in that form in the ash. A mere report of the quantities of the several con- stituents found in the analysis of an ash, will not afford the requisite data for an accurate comparison of the results with those of other analyses, as it includes, or may include, certain substances which are altogether foreign to the purpose for which the ash is analysed, more especially charcoal and sand. To render practicable a comparison of the results severally obtained in different analyses, these unessential and accidental admixtures (charcoal and sand) must be struck out, and the remaining constituents of the ash calculated in per-centage parts. A report intended to show the composition of an ash as revealed by the analytical process, must include the carbonic acid among the essential constituents ; but if the object of the analysis is to ascertain what are the inorganic salts which a plant derives from the soil, the carbonic acid must be struck out of the calculation, as well as the charcoal and sand. To satisfy every requirement, it is best to state the results both ways, i.e., inclusive and exclusive of the unessential parts ; the first statement will enable chemists to judge of the degree of accuracy of the analysis, the other will facilitate comparisons. If the carbonic acid is omitted from the second report, for the reason stated, the quantity of carbonic acid contained in 100 parts of the ash must be mentioned instead. II. Q Q 594 ANALYSIS or SOILS. [ 256, 257. D. CALCULATION OF THE PER-CENTAGE PROPORTION WHICH THE SEVERAL CONSTITUENTS OP THE ASH BEAR IN THE COMPOSITION OF THE PLANT, OB PART OF A PLANT, WHICH HAS FURNISHED IT. 256. The usual way formerly was to incinerate, with proper caution, a small weighed portion of the carefully dried vegetable substance, and determine the total amount of the ash ; and then to incinerate a lai'ger unweighed portion, less carefully dried, and analyse the ash obtained. A simple calculation then sufficed to find the per-centage proportions of the several constituents. For instance, some grains of wheat had left upon incineration 3 per cent, of ash, containing 50 per cent, of phosphoric acid : 100 parts of these grains of wheat were therefore assumed to con- tain 1 -5 per cent, of phosphoric acid, &c. This method is unquestionably most convenient ; but, unfortunately, it does not give sufficiently accurate results in all cases, since, from the causes stated in 250, the total amount of the ash is by no means con- stant, but varies more or less, within certain limits, according to the manner, intensity, and duration of the process of ignition. As we can, therefore, in most cases, never be sure that the smaller portion obtained in the determination of the total weight of the ash, corresponds exactly in composition, &c., with the larger portion used in the actual analysis, it is always the safer plan to weigh, as I have already recommended in 250, on the one hand, the total quantity of the (dried) substance intended for incineration, and, on the other hand, the total amount of ash obtained and intended for analysis. If it is wished to avoid this, the end in view may also be attained in another manner, viz., by incinerating first a large unweighed portion of the vegetable substance, analysing the ash, and determining thus the relative proportions between the several constituents ; then incinerating a smaller weighed portion, dried at 212 F., and determining in the ash one of those constituents which are not liable to the least change in quantity from the mode of incineration lime, for instance. As the relative quantity of this substance in the composition of the plant is known, as well as the proportion between it and the other constituents of the ash, it is easy to calculate from these data also the per-centage proportions which the other constituents of the ash bear in the compo- sition of the plant. IV. ANALYSIS OF SOILS. 257. THE proposition being fully established that every plant requires for its growth and development certain inorganic matters which are supplied by the soil in which it grows, it is self-evident that the knowledge of the composition of the soil must be a subject of paramount importance to the practical farmer, to enable him, on the one hand, to judge to what kind of plants a given soil will afford the requisite nutriment, and, on the other hand, to adapt a soil for the cultivation of a certain plant by a proper supply of the necessary manure. 258.] ANALYSIS OF SOILS. 595 It was hitherto considered that to judge of the fertility of a soil, it was sufficient to know irrespective of the physical conditions which of the constituents would dissolve in water, which in dilute acids, and which in neither of these solvents. It was assumed that the substances soluble in water were supplied direct to the plant with the water absorbed from the soil ; whilst those soluble in dilute acids were made available by the agency of carbonic acid and salts of ammonia ; and the insoluble substances, lastly, were only slowly and gradually prepared, by progressive disintegration and decomposition, to serve as nutriment for plants. Liebig ("On Modern Agriculture," Letters III. and VIII., Wal- ton and Maberly) has lately refuted this view of the nutrition of plants ; he admits, indeed the co-operation of the solvents named, but he attributes to the roots of the plant an inherent faculty of with- drawing and appropriating from the soil substances which neither pure water nor water impregnated with carbonic acid would be able to withdraw. Indeed, arable soil exercises, in a certain sense, a similar action to that of porous charcoal, withdrawing, like the latter, from fluids, sub- stances which they hold in solution, as, e.g., ammonia from ammoniacal solution, silicic acid and potassa from solution of soluble glass, phosphate of ammonia and magnesia from its solution in water impregnated with carbonic acid, &c. ; which of course sufficiently proves that these substances cannot be withdrawn from the soil, at least not completely, by water, or water impregnated with carbonic acid. Now, although the way in which plants take up the inorganic con- stituents of their food from the soil is not as yet clearly established, this much is certain, that a mere knowledge of the different degrees of solubility of the several constituents will not enable the agricultural chemist to judge of the fertility of a soil ; that no useful inferences can be drawn from the component parts of an aqueous extract of the same ; and that the state of mechanical division in which the several constituents exist in the soil is of as great importance as the state of solubility. Besides the inorganic constituents, there are found in most, in fact nearly in all soils, organic substances (vegetable and animal remains and the products of their decomposition). That these organic substances exercise a material influence on the fertility of the soil is unquestionable ; and, whatever views may be entertained as to the manner of this in- fluence, this much is certain, that it is highly important to obtain also a knowledge of the nature and quantity of the organic constituents con- tained in a soil. The old methods of analysing soils by preparing aqueous extracts, &c., and examining them, are of course no longer applicable ; the analytical process is now properly divided into two parts, viz., I., Mechanical Analysis, and, II., Chemical Analysis. I. MECHANICAL ANALYSIS OF THE SOIL (Fr. Schulze, " Journ. f. prakt. Chem., 47, 241). 258. 1. Take samples from different parts of the field, mix intimately, and dry in the air. If the soil contains pebbles or stones, weigh the total quantity of the sample, then pick out the stones and weigh them. Kee r > the air-dried soil in a wide-mouthed stoppered bottle. Q Q 2 596 ANALYSIS OF SOILS. [ 258. 2. Expose 100 grammes of the air-dried soil to the heat of a water- bath (212 F.) until no further diminution of weight is observed, then weigh. The loss of weight shows the amount of moisture ; calculate this for 100 parts of the dried soil. Suppose, for instance, the air- dried soil is found to consist of 96 parts of dried soil and 4 parts of moisture, 4'17 parts of moisture are calculated for 100 parts. Keep the dried soil for chemical analysis (see II.). 3. Crush the air-dried soil with the hand, if caked, and weigh off a quantity exactly corresponding to 1000 grammes of soil dried at 212 F. Pass this through a wire sieve with meshes 3 millimetres in diameter, fitted on to a bottom for collecting the particles passing through the meshes. As soon as this operation is completed, remove the sieve from the bottom, and place it in a dish (A), pour in water sufficient to cover the contents of the sieve, and wash by hand until the clay is completely separated from the gravel ; then rinse the latter thoroughly with water, transfer the contents of the sieve to a dish, dry at 212 F., and weigh. When thoroughly dry, it is then ignited in the air, and the loss of weight indicates the amount of organic matter mixed with the gravel. 4. Pass the product of the first sifting through another wire sieve with meshes 0'66 millimeti'es in diameter, collecting the particles passing through in the bottom, as in the first operation. Remove the sieve, place it in a dish (B), pour in the contents of A, rinse thoroughly with water, adding the rinsings to the contents of B. Wash the earth in the sieve with water until the clay is completely separated from the gravelly sand ; then wash the latter thoroughly with water, transfer to a dish, dry at 212 F., and weigh. If the latter is then ignited in the air, the loss of weight indicates the amount of organic matter mixed with the graveUy sand. 5. The results of the preceding operations show how much 1000 grammes of earth dried at 212 F. contain of a. Gravel, determined by direct weighing ; b. Gravelly sand, { Coarse sand, ~| fine sand | estimated co n ec tively by the difference, since elutriation, J 6. To effect the separate determination of each of the component parts of c, the soil which has passed through the fine sieve must be elutriated. The apparatus described 236, A (Mechanical Analysis of Clays), is used for this purpose. Dry about 40 grammes of the product of the second sifting at 212 F., weigh off 30 grammes of the dried soil, transfer to a porcelain dish, add twice or three times the quantity of water, stir, and boil for half an hour. If the soil is very clayey, a porcelain pestle should be used for stirring, instead of a glass rod, and the operation frequently repeated, to ensure the complete separation of the clay from the sand. Transfer the mass after cooling, to the elutriating glass, with proper i-insing, and remove first the clay and fine sand from the coarser sand, then the clay from the fine sand, in the exact manner directed 236, A (Mechanical Analysis of Clays). The fine sand and the coarse sand are dried at 212 F., weighed, and then ignited with free access of air ; the loss of weight severally observed indicates 259.] ANALYSIS OP SOILS. 5S7 the amount of oi-ganic matter mixed respectively with the coarse sand and the fine sand. 7. Deduct from the 30 grammes boiled with water, a the coarse san,d, b the fine sand ; the difference shows the quantity of the finest particles removed by the process of elutriation, including a certain, though very trifling, proportion of soil dissolved by the elutriating water. Calculate the several quantities of coarse sand, fine sand, and finest elutriated particles found in the 30 grammes, for the total amount of these three constituents found in 1000 grammes of the soil dried at 212 F. (com- pare 5, c) ; and enter the weights found in the report of the results sub 5, c ; then, by removing the decimal point, convert the per mils, into per cents. 8. The results of the mechanical analysis are properly reported as follows : 100 parts of the soil dried at 212 F. contain (by way of illustra- tion) say : Combustible Fixed substances, or volatile substances. . f Gravel, ignited ........ 6'90 Organic matter mixed with it ... . . O'OO Gravelly sand, ignited ..... 6'43 Oranic matter mixed with it . . . 0'67 35-50 Coarse sand > ig nited ...... 3 *'37 ( Organic matter mixed with it ... . . 1*13 ' An f\(\ I Fine sand, ignited ...... 38-50 | Organic matter mixed with it ... '' ' ; . 1'50 , Finest elutriated particles .... 9 '50 10 '50 I Organic matter mixed with it, am- J monia salts, and chemically com- * bined water . . . ..... . . I'OO 100-00 95-70 4-30 2-10 stones in 100 parts of dried soil. 4-17 moisture calculated to have been present in a quantity of air- dried soil, corresponding to 100 parts dried at 212 F. II. CHEMICAL ANALYSIS. 259. If the chemical analysis of a soil were pushed to the utmost limit indicated in 257, it would be necessary to examine each of the component parts separated by the mechanical process, and accordingly to take into consideration also the substances dissolved by the water of elutriation. However, it is generally sufficient for agricultural pur- poses to confine the analysis to the following processes : 1. Mix the several samples of soil taken from different parts of the field intimately, dry at 212 F., and heat 100 grammes of the dried soil, with access of air, to feeble ignition (best in a flat vessel of clay, porcelain, or silver, placed in a muffle), until the organic matters are completely destroyed ; saturate the residue, after cooling, with a concentrated solution of carbonate of ammonia, dry at a gentle heat, raising the temperature finally to a somewhat higher degree, 598 ANALYSIS OF SOILS. [ 259. to ensure the complete expulsion of the water and carbonate of ammonia, let the residue cool, and, when cold, weigh. The diminu- tion of weight indicates the total quantity of the organic substances, ammonia salts, and the chemically combined water. Pass the ignited residue through the wire sieve with meshes 0'66 millimetres diameter ( 258, 4), to separate the gravel and gravelly sand from the finer par- ticles (the sand, fine sand, and finest particles of clay). Wash the gravel and the gravelly sand, to remove the still adhering soil, and dry. The coarser and the finer parts so separated are then severally analysed, fractional portions being taken of each, and the results calculated for 100 parts. 2. Weigh off 20 grammes of the gently ignited finer portion of the soil, add water, then hydrochloric acid in moderate excess, heat gently for some time on the water bath, filter* into a half-litre flask, wash until the last washings no longer show an acid reaction, then fill with water to the mark, and mix. a. Dry the residue, ignite gently, weigh, then treat with concentrated sulphuric acid as directed 236, B, 2nd method, b. Should the separated sand be found upon examination to be other than pure quartz sand, another portion of it must be analysed in the way usually employed for silicates. b. Measure off 4 several portions of the hydrochloric acid solution, of 50 or 100 c.c., according to the greater or less proportion of certain constituents present. In a, determine the sulphuric acid as directed 1 32, I. In ft, the phosphoric acid as directed 134, b, ft. In y, the iron as directed 113, 2, a.\ In S, the silicic acid, alumina, protoxide of manganese, lime, magnesia, potassa, and soda. Separate first the silicic acid ( 140, II., a), then the sesquioxide of iron, alumina, protoxide of manganese, lime, magnesia, and alkalies, by one of the methods given in 161; if much iron is present, by 161, 2 (96)- Bear in mind that with the sesquioxide of iron and alumina, the whole of the phosphoric acid is also thrown down by acetate of ammonia, and that, therefore, in order to find the alumina, both the sesquioxide of iron found in y and the phosphoric acid found in /3, must be subtracted from the ignited and weighed precipitate. 3. Determine the carbonic acid in a separate portion of the gently ignited finer part of the soil, see (1), as directed 139, II., e, a, bb. 4. Treat portions of the gravel and coarse sand obtained in 1, in the same way as the finer particles in 2 and 3. A further analysis of the part insoluble in hydrochloric acid may often be dispensed with, as the nature of the fragments of stone, &c., can be determined in the minera- logical way. There remains now still, besides the determination of the organic matter, that of the ammonia, chlorine, and nitric acid. Although it may be assumed that these constituents are present only in the sifted finer * To guard against obstruction of tbe filter, it is advisable to transfer first the coarser fragments to it, before pouring on the fluid with the mechanically suspended finer par- ticles of clay. f If the soil contains protoxide of iron, extract a separate portion of the non-ignited finer part with hydrochloric acid, and then determine the protoxide of iron in the solution, as directed 112, 2, a. Calculate this upon the weight of soil contained in 7, and deduct the result from the total quantity of iron found in 7 ; the difference gives the quantity of iron present as sesquioxide. 259.] ANALYSIS OF SOILS. 599 part, yet it is always advisable to use, for these analytical processes, the unsifted soil. 5. Boil a tolerably large portion of the air-dried soil (which must be calculated upon soil dried at 212 F.), with dilute milk of lime, best in a small copper still, and determine the expelled ammonia by BoussingaulCs method, 209, 8. 6. To determine the chlorine, treat a portion of the soil dried at 212 F. with highly dilute nitric acid in the cold, and precipitate the solution, with solution of nitrate of silver ( 141, a). 7. To determine the nitric acid, extract a weighed portion of the air- dried soil (which must be calculated upon soil dried at 21 2 F.), as completely as practicable with water, and treat the extract as directed 209, 9. Should the presence of larger proportions of organic matters prevent the use of the method described 149, II., a, a, the method ;3 or y, must be employed. The aqueous extract may be prepared, either strictly according to the directions of 214 of Fresenius's "Qualitative Analysis," or in the following manner,* which requires the xise of a three-necked Woulfs bottle, provided also with a lateral tubulated orifice in the lower part. A wide glass cylinder open at the top and narrowing towards the lower end (a percolator), which holds about 1000 grammes of soil, fits air-tight into the middle neck. Push down into the narrow part of the percolator a loose plug of sponge, spread over this a layer of pure sifted gravel, cover the latter with a thick layer of washed fine sand, and then introduce the soil. Fit a tube connected with a hand air-pump into one of the other necks, and close the third neck and the lower opening. Moisten the soil with water, pouring on from time to time a fresh quantity, and continuing in this way for 24 hours ; then rarefy the air in the bottle by means of the hand-pump, which will force the water charged with the soluble parts of the soil more rapidly from the percolator into the bottle. When the latter is nearly full, remove the stopper from the third neck, place a vessel under the lower opening to receive the fluid, and then remove the stopper, f The solution so obtained is per- fectly clear. 8. Determination of the Acids of Humus\ (Uhnic, Humic, Ge'ic Acids}. Digest from 10 to 100 grammes of the air-dried soil (according as the qualitative analysis has shown the presence of a smaller or greater quantity of the acids of humus) for several hours, at 176 194 F., with a solution of carbonate of soda ; filter. Mix the filtrate with hydrochloric acid to slightly acid reaction ; the acids of humus will separate in the form of brown flakes. Collect these flakes on a weighed filter, wash until the water just appears colored ; dry, and weigh. Burn the dry mass, deduct the weight of the ash (after subtracting the filter ash) from that of the dry mass, and enter the difference in the calculation as acids of humus. 9. Estimation of the so-called Humus Coal (Ulmine and Humine). Boil a quantity of soil equal to that taken in e, in a porcelain dish, * Professor Fr. Schulze ; communicated by letter. t If the Woulfs bottle is not provided with a lower tubulature, the fluid is removed with the aid of a siphon. With regard to the estimation of the organic constituents, compare Otto, SprengeFs "Bodenkunde," page 430, &c. ; and also Fr. Schulze, "Journ. f. Prakt. Chem.," vol. 47, p. 241, &c. 600 ANALYSIS OF SOILS. [ 259. for several hours, with solution of potassa, replacing the evaporating water from time to time. Dilute, filter,* and wash. Determine the total amount of the acids of humus present in the same manner as in 8. The difference between the weights obtained respectively in 8 and 9, expresses the quantity of huniic acid which has been formed from the ulmine or humine by the process of boiling with potassa ; enter it in the calculation as humus coal. 10. Determination of the Organic Matter which has not as yet suffered conversion into Humic Add, Humus Coal, or similar Products. Determine the carbon in the soil by the method of organic analysis, either deducting the carbonic acid found in the form of carbonates from the total amount of carbonic acid obtained, or first completely removing the carbonates from the soil by treating with dilute hydrochloric acid and thorough washing, t before proceeding to combustion with oxide of copper. As the oxide of copper need not be very carefully dried, and as the weighing of the chloride of calcium tube is omitted, the process is much simpler than an ordinary organic analysis. According to Fr. Schulze, 58 parts of carbon correspond on an average to 100 parts of organic matter in the soil, and 60 parts of carbon to 100 parts of humus substances. The quantity of carbon corresponding to the humus sub- stances is calculated by the latter proportion (60 : 100), the result de- ducted from the total amount of carbon, and 100 parts of other organic matter are entered for every 58 parts of the difference. J 11. Determination of the Nitrogen in a Soil. The soil contains, besides the nitrogen of the air enclosed within its pores (which is disregarded), nitrogen in three different forms of com- bination viz., ammonia, nitric acid, and organic matter. By determining, by organic analysis, the total quantity of nitrogen contained in a soil, and subtracting from this the nitrogen of the ammonia and nitric acid, we find the quantity of nitrogen present in the organic matter of the soil. The weight of the nitrogen contained in the organic compounds being included already in the results of 10, is not entered in the list as an element of the calculation, but simply by way of information. 12. Determination of Waxy and Resinous Substances. Waxy and resinous substances are found in appreciable quantities in some kinds of soil only. Their determination may be effected in the following manner : Dry 100 grammes of the soil in the water-bath, boil repeatedly with strong spirit of wine, collect the filtrates in a flask, and distil off half the spirit. Let the mixture cool, which will cause the wax to separate. Collect this on a weighed filter, wash with cold spirit of wine, and determine the weight. Evaporate the filtrate (in the last * If the quantity of the humus coal is very considerable, the fluid alone is poured on the filter at first, and the sediment boiled once more with solution of potassa, before it is transferred to the filter. t The quantity of organic substance dissolved in this process is mostly so trifling that it may safely be disregarded. + If the determination in the bulk of the organic matter present in a soil is deemed sufficient, the chemist may omit the processes 8, 9, and 12, confining the analysis, in this respect, to the estimation of the total amount of carbon, according to the direction of 12, entering 100 parts of organic substance for 59 parts of carbon. To determine the organic matter by the loss of weight which the dried earth suffers by ignition, appears to me altogether inadmissible, as the expulsion of water from the clay, &c., must neces- sarily render the results quite unreliable. 259.] ANALYSIS OF SOILS. 601 stage of the process with addition of water) until the alcohol is com- pletely removed ; wash the separated resin with water, dry, and weigh. If the quantity of wax and resin is in any way considerable, it must be deducted from the weight of the acids of humus, as the latter have been weighed inclusive of the waxy and resinous matters. 13. The remits of the chemical analysis of a soil should be arranged in the manner best calculated to give a correct view of the composition of the soil. I think the following plan best suited for the purpose. The numbers are only given for a few of the constituents, by way of illustration. They are of course arbitrary ; but they correspond as far as practicable with those assumed, by way of illustration, in the arrange- ment of the results of the mechanical analysis. 100 parts of soil dried at 212 F. contain : ''Lime . . . 1-70 Gravel and gravelly sand, 13-33, Soluble in hydrochloric - acid, Insoluble in hydrochloric I Sesquioxide of iron, | Carbonic acid, v. Phosphoric acid, &c. Quartz gravel, slate, 7-00 95-70 acid, 1 Fixed substances, Soluble in 1 hydrochloric ' Lime, i Magnesia, 1 Carbonic acid, acid, vi-j.j ..Phosphoric acid, EXEECISES FOE PRACTICE. B. COMPLETE ANALYSIS OP SALTS IN THE GRAVIMETRICAL WAT ; CALCU- LATION OF THE FORMULA FROM THE RESULTS OBTAINED. ( 202, sqq.) 7. CARBONATE OF LIME. Heat pure carbonate of lime in powder (no matter whether calcareous spar or artificially prepared carbonate of lime) gently in a platinum crucible. a. Determination of the Lime. Dissolve, in a covered beaker, about 1 gramme in dilute hydrochloric acid, heat gently until the carbonic acid is completely expelled, and determine the lime as directed 103, 2, b. b. Determination of the Carbonic Acid. Determine in about 0*8 grm. the carbonic acid according to the directions of 139, II., d. For the composition, see 73. 8. SULPHATE OF COPPER. (Complete Analysis of Sulphate of Copper.) Triturate the pure crystals in a porcelain mortar, and press the powder between sheets of blotting paper. a. Determination of the Water of Crystallization. Weigh an empty bulb tube, and half fill the bulb with sulphate of copper ;* weigh again, then place the tube in an air-bath with openings in its sides (Fig. 33), and proceed as directed 29. When no more water escapes at 248 to 284 F., and repeated weighings of the bulb tube give constant results, the diminution of weight expresses the amount of crystallization water in the salt. A common glass tube of sufficient width may be used instead of a bulb tube, the sulphate of copper being placed in a little boat, and the latter inserted into the tube. To guard against the reabsorption of water during the process of weighing, the little boat should be placed in a small tube, closed by a cork, and this tube weighed with it both before and after weighing. b. Determination of the Water of Halhydration. Proceed with the same experiment, but at a temperature raised to between 482 F. and 500 F. The additional loss of weight of the bulb tube suffered in this process, gives the amount of the more strongly combined halhydratiou water. c. Determination of ilie Sulphuric Acid. In another portion of the sul- phate of copper (about 1-5 grm.) determine the sulphuric acid according to the directions of 132, I., 1. d. Determination of the Oxide of Copper. In about 1 -5 grm. determine the oxide of copper as directed 119, 1, a, a. CuO . . 496-0 . . . 39-68 . . . 31-83 SO. . . 500-0 . . . 40-00 . . . 32-08 HO . . 112-5 . . . 9-00 . . . 7-22 4 aq . . 450-0 . . . 36-00 . . . 28-87 1558-5 124-68 100-00 * This is effected by pushing into one end of the tube, down to the bulb, a glass rod with paper folded round it, and filling in the salt through the other end. The tube is then restored to a horizontal position, and the bulb gently tapped on the table j the glass rod is withdrawn, and the ends are, if necessary, cleaned with a feather. EXERCISES FOB, PRACTICE. 619 9. CRYSTALLIZED PHOSPHATE OF SODA. a. Determination of the Water of Crystallization. Heat about 1 grm. in a platinum crucible, slowly and gently (not to ignition) ; the loss of weight gives the amount of water of crystallization in the compound. 6. Determination of the Basic Water. Ignite the residue of a. c. Determination of the Soda and the Phosphoric Acid. Treat the residue of b as directed 135, a, y. d. Determination of the Phosphoric Acid by way of Control. Treat 1'5 2 grins, of the salt as directed 134, I., b, a. PO 5 . . 887-50 . . 71-00 . . 19.83 2NaO . 774-88 . . 62-00 . . 17-32 HO . . 112-50 . . 9-00 . . 2-51 24 aq . 2700-00 . . 216-00 . . 60-34 4474-88 358-00 100-00 10. PHOSPHATE OF AMMONIA AND MAGNESIA. Dry in the exsiccator (see 27, at the end). a. Water and Ammonia. Ignite about 1 grm. of the salt, and deter- mine the loss of weight. 6. Ammonia. Treat about 1 grm. of the salt as directed 99, 2 ( method /3). c. Phosphoric Acid. Treat about 1 grm. of the salt as directed in 134, c, and about 0-5 grm. as directed 134, b, ft. d. Magnesia. Treat about 1 grm. of the salt as directed 135, d. P0 5 . . 887-50 . . 71-00 . . 28-98 2MgO . 500-38 . . 40-00 . . 16-33 NH 4 . 325-06 . . 26-00 . . 10-61 12 aq . 1350-00 . . 108-00 . . 44-08 3062-94 245-00 100-00 11. CINNABAR. Reduce to a fine powder by trituration, and dry at 212 F. a. Determination of the Sulphur. Pour strong hydrochloric acid over about 0-5 grm. of the sulphide, in a little flask, add from time to time small portions of chlorate of potassa, expose for some time to the action of a very gentle heat, with proper escape for the vapors, and proceed as directed 148, II., , ft. b. Determination of the Mercury. Dissolve about - 5 grm. as before, dilute, and let the mixture stand in a moderately warm place until the smell of chlorine has nearly gone off; filter if necessary, add ammonia in excess, heat gently for some time, add hydrochloric acid until the white precipitate of chloride of mercury and amide of mercury is redissolved, and treat the solution, which now no longer smells of chlorine, as directed 118,3. For the per-centage composition, see 84, c. 12. CRYSTALLIZED GYPSUM. Select pure native crystallized gypsum, triturate, and dry under the exsiccator ( 27). EXERCISES FOR PRACTICE. a Determination of Water. See 35, a, a. b. Determination of Sulphuric Acid and Lime ( 132, II., b, a). CaO . . .350 . .28 . . 32-56 SO S . . . 500 . .40 . . 46-51 2 aq. . . .225 . .18 . . 20-93 1075 86 100-00 C. SEPARATION OF TWO BASES OR TWO ACIDS FROM EACH OTHER, AND DETERMINATIONS IN THE VOLUMETRICAL WAY. 13. SEPARATION OF IRON FROM MANGANESE. Dissolve in hydrochloric acid about 0*5 grm. of fine pianoforte wire, and about the same quantity of ignited protosesquioxide of manganese (prepared as directed 109, 1) ; heat with a little nitric acid, and separate the two metals by means of acetate of soda ( 160, 80). Determine the manganese as directed 109, 1, a. 14. VOLUMETRIC DETERMINATION OF IRON BY SOLUTION OF PERMANGANATE OF POTASSA. a. Determination of the Strength of the Solution of Permanganate of Potassa. a. By metallic iron, 112, 2, a, aa. /3. By sulphate of protoxide of iron and ammonia, 112, 2, a, a, bb. y. By oxalic acid, 112, 2, a, a, cc. b. Determination of Iron in Brown Hematite ( 240). 15. DETERMINATION OF NITRIC ACID IN NITRATE OF POTASSA. Dry at 212 F. Proceed as directed 149, II, a, a. For the per-centage composition, see 68,. b. 16. SEPARATION OF MAGNESIA FROM SODA. Dissolve in dilute hydrochloric acid about 0-4 grm. of pure recently ignited magnesia* and about 0*5 grm. of pure fused chloride of sodium, and separate the alkali from the earth, by means of oxalic acid, as directed 153 (18). 17. SEPARATION OF POTASSA FROM SODA. Press between blotting paper, triturated crystallized tartrate of potassa and soda (Rochelle salt), weigh off about 1 -5 grm., heat in a platinum crucible, gently at first, then to ignition, and complete combustion of the separated charcoal. Dissolve the residue in water, determine the alkalies jointly as chlorides ( 97, 3), then separate them by bichloride of platinum ( 152, 1), and calculate from the results the quantities of soda and potassa severally contained in the Rochelle salt KG ... 588-86 . . 47-11 . . 16-70 NaO . . . 387-44 . . 31-00 . . 10-99 C 8 H 4 10 . . . 1650-00 . . 132-00 . . 46-79 8aq . . 900-00 . . 72-00 . . 25-52 3526-30 282-11 100-00 * This may be prepared most readily by exposing pure oxalate of magnesia to the action of heat (P. Schulze). EXERCISES FOR PRACTICE. 621 18. YOLUMETRICAL DETERMINATION OP CHLORINE IN CHLORIDES. a. Preparation and examination of the solution of chloride of sodium and nitrate of silver ( 141, I., b, a). b. Indirect determination of the soda and potassa in Rochelle salt, by volumetrical estimation of the chlorine in the alkaline chlorides prepared as in No. 17. Calculation, see 200, a, ft. 19. SEPARATION OF ZINC FROM CADMIUM. Dissolve in hydrochloric acid about 0*4 grm. of pure'oxide of cadmium, and about the same quantity of pure oxide of zinc, both recently ignited, and separate the metals as directed 162 (107)> 20. ACIDIMETRY. a. Preparation of standard oxalic acid, standard sulphuric acid, and standard solution of soda( 215). b. Determination of free acid in hydrochloric acid, by the specific gravity ( 209 and 214, Table II.). c. Determination of free acid in the same hydrochloric acid, by satura- tion with an alkaline fluid of known strength ( 215). d. Determination of free acid in colored vinegar, by saturation with an alkaline standard solution (application of test papers). e. Preparation of an ammoniacal solution of sulphate of copper (216); determination of its strength by standard sulphuric acid ; estimation of the free acid in the hydrochloric acid used in b and c, by means of the ammoniacal solution of sulphate of copper ; in this latter process the student may also add to the hydrochloric acid, some neutral sulphate of zinc. 21. ALKALIMETRY. a. Preparation of the test acid by Descroizelles and Gay-Lussac's process ( 219). b. Estimation of potassa in potash of commerce after expulsion of the water by gentle ignition. a. By ^Descroizelles and Gny-Lussacs method ( 219). 0. By Mohr's method ( 220). 22. DETERMINATION OF AMMONIA. Treat about 0*8 grm. of chloride of ammonium as directed 99, 3, a. For the per-centage composition, see 70. 23. SEPARATION OF MERCURY FROM LEAD. Dissolve about 0'5 grm. of chloride of mercury and about 1 grm. of crystallized acetate of lead, and separate the metals as directed 163 (132, 133). 24. SEPARATION OF IODINE FROM CHLORINE a. Dissolve about 0-2 grm. of iodide of potassium and about 0'6 grm. of chloride of sodium, and determine the iodine and chlorine in the mix- ture as directed 169 (222). Calculation, see 200, c. b. Determine in a similar mixture the iodine and chlorine as directed 169 (225). 622 EXERCISES FOR PRACTICE. D. ANALYSIS OF ALLOYS, MINERALS, PRODUCTS OP INDUSTRY, &c., IN THE GRAVIMETRICAL AND VOLUMETRICAL WAY. 25. ANALYSIS OF BRASS. Brass is a compound of from 25 to 35 per cent, of zinc and from 65 to 75 per cent, of copper. Besides these two essential constituents, it contains usually also small quantities of tin and lead. a. Dissolve about 2 grammes in nitric acid. Do not use more of the acid than is absolutely necessary, as the excess must be driven off by evaporation. If an insoluble residue remains (binoxide of tin), filter the fluid after previous dilution with water from this residue ( 164, 148)- Add to the filtrate, or, if the quantity of the tin is only very inconsiderable, directly to the solution, about 20 c.c. of dilute sulphuric acid ; evaporate the mixture to diyness on the water-bath, add 50 c.c. of water, and apply heat. If a residue remains (sulphate of lead), filter, and proceed as directed 116, 2. In the filtrate, separate the copper from the zinc by hyposulphite of soda as directed 162 (112). b. In about 1 grm. of the alloy determine, after removal of the tin and lead as in a, the copper as directed 119, 2. 26. ANALYSIS OF SOLDER (TIN AND LEAD). Introduce about 1 '5 grm. of the alloy, cut into small pieces, into a flask, pour nitric acid over it, and proceed as directed 164 (148)? to effect the separation and estimation of the tin. Mix the filtrate in a porcelain dish with pure dilute sulphuric acid, evaporate the nitric acid on the water-bath, and proceed with the sulphate of lead obtained as directed 116, 2. Test the fluid filtered from the sulphate of lead with sulphuretted hydrogen and sulphide of ammonium for the other metals which the alloy might contain besides tin and lead. 27. ANALYSIS OF ALLOYS OF SILVER AND COPPER. Determine the silver by the volumetrical method ( 115, 5). 28. ANALYSIS OF A DOLOMITE. See 237. 29. VOLUMETRICAL DETERMINATION OF LIME IN CALCAREOUS SPAR. See 223. 30. ANALYSIS OF FELSPAR. a. Decomposition by carbonate of soda ( 140, II., 6) ; removal of the silicic acid ; separation of the alumina from the small quantity of sesqui- oxide of iron usually present, by one of the methods recommended for the purpose in 160. b. Decomposition by hydrofluoric acid gas ( 140, IT., b, ft) ; determi- nation of the potassa. After evaporating with sulphuric acid and dis- solving the residue in hydrochloric acid and water, add, cautiously, chloride of barium us long as a precipitate forms, then without filter- ing carbonate of ammonia. and ammonia. Let the precipitate subside in the cold, then filter, evaporate the filtrate to dryness, ignite the EXERCISES FOR PRACTICE. 623 residue to expel the ammonia salt ; add again carbonate of ammonia and ammonia to effect the precipitation of the baryta still remaining in solu- tion, and determine the potassa finally as directed 97, 3. 31. ANALYSIS OP GALENA. a. Determination of the sulphur, lead, iron, &c., as directed 242. b. Determination of silver in galena by cupellation ( 243). 32. ANALYSIS OF MIXED SILICATES. See 235. The special plan of proceeding is left to the judgment of the student. 33. ANALYSIS OF CLAYS. See 236. 34. ANALYSIS OF MINERAL WATERS. See 206 213. The determination of constituents present only in very minute quantities may be omitted. 35. ANALYSIS OF ASHES OF PLANTS. See 249256. 36. ANALYSIS OF SOILS. See 257259. 37. DETERMINATION OF CHLORINE IN CHLORIDE OF LIME ( 224). a. By Proofs method ( 227). b. By BunsevUs method. a. Preparation of the iodine solution, 146. ft. Determination of the strength of the iodine solution. aa. By pure iodine ( 146, 1, c, (3, CM), bb. By chromate of potassa ( 146, 1, c, ft, bb). y. Examination of chloride of lime (see D, 228). 38. DETERMINATION OF BINOXIDE IN MANGANESE ORES ( 229). a. By Fresenius and Witts method (230, A). b. By Bunseris method ( 230, B). c. By means of iron ( 230 C). 39. ANALYSIS OF GUNPOWDER. See 234. :'; ^ : 40. DETERMINATION OF SUGAR IN FRUIT, HONEY, MILK, 2 c.c. 14 c.c. 6-70 2c.c. 14 c.c. 7-40 solution of : ^ chloride of ammonium 6 c.c. (1 : 10) 10 c.c. 7-00 water 1 4 c.c. ,' 2 c.c. r ,SO,dil. (1:5) 8 c.c. 7 30 <^ NH 4 0, NO. (1:10) 1 6 c.c. water 648 APPENDIX. antimony, = 43-29 per cent, of teroxide of antimony. As tartrate of anti- mony and potassa contains 43-39 per cent, of teroxide of antimony, the process gives, if the precipitate is dried at 212 F., 102-5 ; if heated to blackening, 99*77 instead of 100. 77. DEPORTMENT OF A HYDROCHLORIC ACID SOLUTION OF TEROXIDE OF ANTIMONY WITH OXIDIZING AGENTS (to 125, 3). Three portions, of 10 c.c. each, of a solution of teroxide of antimony prepared with the least possible quantity of hydrochloric acid, and contain- ing about 0'05 grm. of teroxide in 10 c.c. of solution, were mixed severally with 20 c.c. of hydrochloric acid, of 1'12 sp. gr., and different quan- tities of water ; solution of permanganate of potassa was then added until the fluid appeared red. Amount of water added. 250 c.c. 16-2 400 c.c. 16-7 500 c.c. 17-95 10 c.c. of hydrochloric acid and 500 c.c. of water being added to 10 c.c. of the same solution of antimony, 22*6 c.c. of solution of permanganate of potassa were required. Bichromate of potassa exercised the same action upon hydrochloric acid solution of teroxide of antimony. 78. YOLUMETRICAL DETERMINATION OF ANTIMONY (to 125, 3). 5 - 0822 grms. of chemically pure tartrate of antimony and potassa were dissolved to 250 c.c. Four portions of this solution, of 10 c.c. each, were mixed severally with different quantities of a cold saturated solution of pure bicarbonate of soda, and with different quantities of water ; after addition of 2 c.c. of starch paste to each portion, solution of iodine (100 c.c. = 0'53064 of iodine, corresponding to 0-30154 of teroxide of antimony) was dropped in until the iodide of starch reaction made its appearance in the several fluids. 1. 10 c.c. of the solution of tartrate of antimony and potassa + 5 c.c. of solution of Na 0, 2 C O 2 ; it took 29-9 c.c. of iodine solution to impart to the fluid a reddish color, which did not instantly disappear upon shaking; and 30-1 c.c. to produce a distinct blue tint ; after some time, the latter also disappeared. 2. 10 c.c. of the tartar emetic solution + 10 c.c. of solution of NaO, 2 CO 2 . After addition of 29-2 c.c. of iodine solution, the fluid just began to exhibit a red tint, which immediately disappeared ; 29 - 4 c.c. produced a distinct blue color, which disappeared only after 15 minutes. 3. 10 c.c. of the tartar emetic solution 4- 20 c.c. of solution of Na 0, 2C0 2 . After addition of 29-2 c.c. of iodine solution, the fluid just began to exhibit a red tint; 29-5 c.c. produced a distinct blue color, which dis- appeared only after 15 minutes. 4. 10 c.c. of tartar emetic solution + 20 c.c. of solution of NaO, 2 C O 2 + 100 c.c. of water. The results obtained were exactly the same as in 3. The results of the three last experiments, therefore, agreed very well, and as 29-5 c.c. of iodine solution correspond to 0-08895 of teroxide of antimony, which are contained in 020329 of tartrate of antimony and potassa, the two last experiments give 43'75 per cent, of teroxide of antimony in tartar emetic. The formula demands APPENDIX. 649 (Sb= 120-2) 43-39. If the first reddening of the fluid which remains visible for a short time after stirring is considered as the final reaction, only 29-2 c.c. of iodine solution were required, which gives 43-31 of teroxide of antimony in tartar emetic. 79. ACTION OP IODINE SOLUTION UPON SOLUTION OF CARBONATE OF SODA (to 125, 3). A solution was used of pure carbonate of soda, perfectly free from re- ducing substances,* which contained 5 grammes of anhydrous salt in 100 c.c. of fluid. The iodine solution contained 0*53064 grm. of iodine in 100 c.c. of fluid. The temperature was 67'1 F. The quantity of starch paste added to each sample was 2 c.c. The two stages marked of the re-action were : a. The point at which the fluid just began to exhibit a faint blue tint. b. The point at which the fluid presented the same blue color as a mix- ture of 30 c.c. of water with 2 c.c. of starch paste, and 1 drop of iodine solution. Solution of Solution of iodine used to NaO, C,0, Water. produce the reaction. a. b. 1. 20 c.c. ... ... 0-2 ... 0-4 2. 20 c.c. ... 60 ... 0-55 ... 0-8 3. 20 c.c. ... 120 ... 0-8 ... 1-2 4. 20 c.c. ... 280 ... 1-7 ... 2-2 Deducting for 1, 1 drop, for 2, 2 drops, for 3, 0-1 c.c., for 4, 0-2 c.c., of iodine solution, being the quantities severally required to impart a blue tint to pure water mixed with starch paste, the results of this series of experiments clearly show that the same quantity of carbonate of soda will prevent the larger amount of iodine from forming iodide of starch, the more considerable the volume of water present. 80. ACTION OF IODINE SOLUTION UPON SOLUTION OF BICARBONATE OF SODA (to 125, 3). The experiments were made with a cold saturated solution of the bi- carbonate, free from simple carbonate of soda and from reducing agents ; the other conditions were the same as in No. 79. Solution of Solution of iodine used to Na 0, 2 C 0,. Water. produce the re-action. a. b. 1. 20 c.c. ... ... ... 1 drop 2. 20 c.c. .. 60 ... 1 drop ... O'Oo 3. 20 c.c. ... 120 ... 0-05 ... 0-10 4. 20 c.c. ... 280 ... 0-10 ... 0-25 The results of this series of experiments clearly show that bicarbonate of soda exercises no influence upon the iodide of starch re-action. 81. DETERMINATION OF ARSENIOUS ACID BY SOLUTION OF IODINE (to 127, 5). 2-5 grammes of pure arsenious acid were dissolved in a solution of pure carbonate of soda, a very slight excess of hydrochloric acid was * Prepared from thoroughly washed bicarbonate of soda. A drop of a dilute solution of permanganate of potassa imparted to 20 c.c. of it a red tint, which did not disappear . upon addition of dilute sulphuric acid in excess. 650 APPENDIX. added to the dilute fluid, which was then further diluted to 250 c.c. The experiments were made at 68 F. The iodine solution contained 0-53064 grm. of iodine in 100 c.c. of fluid. 1. 10 c.c. of this solution + 20 c.c. of a solution of bicarbonate of soda saturated at 68 F. + 2 c.c. of starch paste. It took 49-05 c.c. of the iodine solution to impart a reddish tint to the fluid, which after a short time disappeared ; and 49 '25 c.c. to produce a distinct blue color. 2. Same conditions as in 1, but with addition of 250 c.c. of water; first appearance of a light bluish tint, after addition of 49-1 c.c. of the iodine solution ; distinct blue color, after addition of 49 -25 c.c. 3. Same conditions as in 1, simply substituting for 20 c.c. of solution of bicarbonate of soda, 10 c.c. of solution of perfectly pure carbonate of soda (1 : 20), prepared from thoroughly washed bicarbonate. First, bluish tint, after addition of 49-25 c.c. of iodine solution; distinct blue color, after addition of 49-32 ac. 4. Same conditions as in 3, with 20 c.c. of solution of carbonate of soda instead of 10 c.c. Distinct blue color, after addition of 49-27 c.c. of iodine solution. 5. Same conditions as in 4 + 250 c.c. of water. Distinct blue color, after addition of 49 '3 c.c. of iodine solution. 6. Same conditions as in 5, with 50 c.c. of solution of carbonate of soda instead of 20 c.c. Distinct blue color, after addition of 49 -46 c.c. of iodine solution. These results are quite satisfactory. 49 c.c. of iodine solution were clearly sufficient to convert the arsenious into arsenic acid ; they corre- spond to 0-1014 grm. of arsenious acid, whilst the 10 c.c. of solution used contain 0-1 grm. 82. DETERMINATION OF SULPHURIC ACID BY MEANS OF A SOLUTION OF NITRATE OF LEAD OF KNOWN STRENGTH (to 132, I., 2, 3). Grundinann. 1. 50 c.c. of water, mixed with a few drops of solution of iodide of potassium, required 0'15 of a solution of nitrate of lead, containing 165-57 grm. in 1 litre of fluid. 2. 50 c.c. of a solution of sulphate of potassa, containing 10 grm. of the salt in 1 litre of fluid, requii'ed, after addition of a few drops of solution of iodide of potassium, 5-85, 6'05, and 5-55 of the above solution of nitrate of lead, and accordingly, after deduction of O'lo c.c., 5"7, 5*9, and 5-4, corresponding to 0'495, 0'513, and 0470 of sulphate of potassa instead of 0-500. 3. To ascertain whether better results might be obtained by heating the solution of sulphate of potassa, the following experiments were made with the solution heated in the water-bath : a. 30 c.c. KO, S0 3 + 20 c.c. of water required 3'6-0-15 c.c. Pb 0, N O s . which gives 0-3005 instead of 0'3 K 0, S 0,. b. 70 c.c. KO, S0 3 + 50 c.c. of water required 8-35-0-25 c.c Pb 0, N O 6 , which gives 0-7055 instead of 0-700 K O, S O 8 . c. 10 c.c. KO, SO S + 40 c.c of water required 1-3-0-15 c.c. PbO, "N"0 6 , which gives O'lOOl instead of O'lOO K O, S O s . 83. DETERMINATION OF PHOSPHORIC ACID AS PYROPHOSPHATE OF MAGNESIA (to 134, b, a). 1-9 159 and 2 -0860 grms. of pure crystallized phosphate of soda, treated APPENDIX. 651 as directed 134, b, a, gave 0-5941 and 0-6494 grm. of pyrophosphate of magnesia. This gives 19-83 and 19-91 per cent, of phosphoric acid in phosphate of soda, instead of 19*83 per cent. 84. DETERMINATION OF PHOSPHORIC ACID AS PHOSPHATE OF SESQUI- OXIDE OF URANIUM (to 134, c). 30 c.c. of a solution of pure phosphate of soda, treated with sulphate of magnesia, chloride of ammonium, and ammonia, as directed 134, b, a, gave 0-3269 grm. of pyrophosphate of magnesia. 10 c.c. contained accordingly -06 98 2 grm. of phosphoric acid. 10 c.c. of the same solution were then precipitated with acetate of sesquioxide of uranium as directed 134, c. The ignited precipitate was treated with a little nitric acid, then again ignited ; after cooling, it weighed 0-3478 gramme, corresponding to 0-06954 grm. of phosphoric acid. 85. INFLUENCE OF TEMPERATURE, ETC., UPON THE IODIDE OF STARCH RE-ACTION (to 148, 1., a). See "Anna!, d. Chem. u. Pharm.," 102, 186. 86. DETERMINATION OF FREE SULPHURETTED HYDROGEN BY MEANS OF SOLUTION OF IODINE (to 148, I., a). The experiments were made to settle the following questions : a. Does the quantity of iodine required remain the same for solutions of sulphuretted hydrogen of different degrees of dilution ? b. Does the formula HS + I = HI + S really represent the decom- position which takes place, and may the method accordingly be considered to give correct results ? The sulphuretted hydrogen water was contained in a flask closed by a double-perforated cork ; into one aperture a siphon tube with com- pression clamp was fitted, to draw off the fluid ; into the other aperture a short open tube, which did not dip into the fluid. Question a. a. About 30 c.c. of iodine solution were introduced into a flask, which was then tared ; sulphuretted hydrogen water was added until the yellow color had just disappeared. The flask was then closed, weighed, starch paste added, and then solution of iodine until the fluid appeared blue. 70 -2 grms. of sulphuretted hydrogen water required 2 3 -4 c.c. of iodine solution, 100 accordingly 33-33 c.c. 68-4 grms. required 22'7 c.c. of iodine solution, 100 accordingly 33-20 c.c. /3. Same process ; but the solution of sulphuretted hydrogen was diluted with water free from air. 6 1-5 grms. of sulphuretted hydrogen water + 200 grms. of water required 20-7 c.c. of iodine solution, 100 accordingly 33'65 c.c. 52-4 grms. +400 grms. of water required 17-7 c.c. of iodine solution, 100 accordingly 33'77. The iodine solution contained 0-00498 of solution of iodine in 1 c.c. of fluid. Considering that addition of a larger volume of water necessarily involves a slight increase in the quantity of iodine solution, these results may be considered sufficiently corresponding. Question b. According to a, 100 grms. of H S water contained 0-02215 grm. of H S, assuming the proportion to be 100 : 33'2, 173'6 grms. of the same 652 APPENDIX. water were, immediately after the experiments in a, drawn off into hydrochloric acid solution of arsenious acid ; after 24 hours, the tersul- phide of arsenic acid was filtered off, dried at 212 P., and weighed. It weighed 0-0920 grm., which corresponds to 0-03814 H S, or in per-cents., 0-02197 ; which resolves the second question also in the affirmative. 87. DETERMINATION OF NITRIC ACID BY PELOUZE'S METHOD (to 149, II, a, a). See " Annal. d. Chem. u. Pharm.," 106, 217. 88. DETERMINATION OF NITRIC ACID BY STEIN'S METHOD (to S 149, IL, b). 1-0938 grm. of nitrate of potassa was treated as directed 149, II., 6. The arsenate of magnesia and ammonia, dried at 212 F., weighed 2-0528 grrns., which give 1-0924 of nitrate of potassa- 99-87 instead of 100. 89. SOLUTION OF CHLORIDE OF MAGNESIUM DISSOLVES OXALATE OF LIME (to 154, 4). If some chloride of calcium is added to a solution of chloride of mag- nesium, then a little oxalate of ammonia, no precipitate is formed at first ; but iipon slightly increasing the quantity of oxalate of ammonia, a trifling precipitate gradually separates after some time. If an excess of oxalate of ammonia is added, the whole of the lime is thrown down, but the precipitate contains also oxalate of magnesia. This shows that to effect the separation of the two bases by oxalate of ammonia, the latter reagent must be added in excess ; whilst, on the other hand, the operator must, in that case, be prepared to find oxalate of magnesia in the precipitated oxalate of lime, as the following experi- ments (No. 90) clearly show. 90. EXPERIMENTS ON THE SEPARATION OF LIME FROM MAGNESIA (to 154, 4). The fluids employed in the following experiments were, a solution of chloride of calcium, 10 c.c. of which corresponded to 0-5618 Ca O, C O 2 ; a solution of chloride of magnesium, containing 0-250 MgO in 10 c.c. of fluid ; a solution of chloride of ammonium (1 : 8) ; solution of ammonia, containing 10 per cent. N H 3 ; a solution of 1 part of oxalate of ammonia in 24 parts of water ; acetic acid, containing 30 per cent. A, H O. The precipitation was effected at the common temperature; the precipitate of oxalate of lime was filtered off after 20 hours. a. Influence of the degree of dilution. a. 10 c.c. Mg Cl, 10 c.c. Ca Cl, 10 c.c. N H 4 Cl, 4 drops N H 4 0, 50 c.c. of water, 20 c.c. N H 4 O, O. Result, 0-5705 Ca O, C O 2 . ft. Same as a, with 150 c.c. of water instead of 50 c.c. Kesult, 0-5670 Ca O, C O 2 . b. Influence of excess of ammonia. Same as a, ft, + 10 c.c. N H 4 O. Result, 0-5614 grm. Ca O, C 8 . c. Influence of excess of chloride of ammonium. Same as a, ft + 40 c.c. N H 4 C1. Result, 0-5652 grm. d. Influence of excess of ammonia and chloride of ammonium. Same as a, /3, + 30 c.c. N H 4 C1 + 10 c.c. N H 4 O. Result, 0-5613 grm. e. Influence of free acetic acid. APPENDIX. 653 Same as o, |3, + 4 drops N H 4 O -f 6 drops A. Result, 0-5594 grm. f. Influence of excess of oxalate of ammonia, in feebly alkaline solution. Same as a, ft, + 20 c.c. N" H 4 0, 6. Result, 0-5644 grin. Ca O, C O 2 . g. Influence of excess of oxalate of ammonia, in strongly alkaline solution. Same as in a, ft, + 10 c.c. N H 4 + 20 c.c. N H 4 0, O. Result, 0-5644 grm. h. Influence of excess of oxalate of ammonia, in presence of much N H 4 C1 and N H 4 O. Same as a, ft, + 10 N H 4 O + 30 N H 4 C1 + 20 N H 4 O, O. Result, 0-5709 grm. i. Influence of excess of oxalate of ammonia, in solution slightly acidified with A. Same as a, /3,-4 drops N" H 4 + 6 drops A + 20 c.c. N H 4 O, O. Result, 0-5661 grm. ; which proves that in presence of a notable amount of magnesia there is always a chance of oxalate of magnesia, or oxalate of magnesia and ammonia precipitating along with the oxalate of lime. Another series of experiments made with a solution of oxalate of magnesia in hydrochloric acid to which ammonia in excess was added, proved also that, in presence of a notable quantity of magnesia, oxalate of magnesia, or oxalate of magnesia and ammonia, will always separate after standing for some time, no matter whether in a cold or a warm place. In a third series of experiments, the lime was separated from the magnesia by double precipitation, in strict accordance with the instructions given in 154 [30]- The same solutions were employed as in the first series, with the exception of the chloride of magnesium, for which a solu- tion was substituted containing 0-2182 grm. MgO, in 10 c.c. of fluid. 10 c.c. Ca Cl + 30 c.c.Mg 01, + 20 c.c. N H t Cl, + SOOc.c. water, + 6 drops ammonia, + a sufficient excess of oxalate of ammonia. Results, in two experiments, 0-5621 and 0-5652, mean 0-5636, instead of 0-5618 Ca O, C O 2 ; in two other experiments, 0-6660 and 0-6489 Mg O, mean 0-6574, instead of '654 6. 91. SEPARATION OF COPPER AND CADMIUM FROM ZINC (to 162, A, ft). See "Jour. f. prakt. Chem.," 73,241. 92. SEPARATION OF IODINE FROM CHLORINE BY PISANI'S METHOD (to 169, [225])- 0-2338 grm. of iodide of potassium, dissolved in water, + |- c.c. of solu- tion of iodide of starch, required 14 c.c. of decimal standard solution of nitrate of silver = 0-2322 grm. of iodide of potassium. 0-3025 grm. of iodide of potassium, mixed with about double the quantity of chloride of sodium, required 18-2 c.c. of the silver solution = 0-3021 K I. 0-2266 grm. of iodide of potassium, mixed with about 100 times as much chloride of sodium, required 13'7 c.c. of the silver solution = 0-2272 K I. 93. SEPARATION OF IODINE FROM BROMINE, BY PISANI'S METHOD (to 169, [229])- 0-31 98 grm. of iodide of potassium, mixed with double the quantity of 654 APPENDIX. bromide of potassium, required 19-2 c.c. of decimal standard solution of nitrate of silver = 0-3187 of K I. 94. ACTION OF SULPHURETTED HYDROGEN UPON VARIOUS METALLIC SOLUTIONS SENSIBILITY OF THE RE-ACTION (to 208, 9). To five portions, of 500 c.c. each, of a highly dilute aqueous solution of sulphuretted hydrogen, containing O'OOS H S in 1000 parts of fluid, was added, to, a. Cu Cl, which imparted a blackish color to the fluid. b. As O 3 , dissolved in H Cl, which produced a precipitate only after 1'2 hours ; the fluid had not quite cleared at the time. c. Cd Cl, which gave a fine flocculent precipitate after 1 hour. d. Ag 0, N O 5 . The fluid appeared blackish ; it required 12 hours for the precipitate to subside completely. e. HgCy. The fluid appeared blackish ; it required 12 hours for the precipitate to subside. 95. DETERMINATION OF SULPHURETTED HYDROGEN BY SOLUTION OF CADMIUM (to 208, 9). 230'3 grammes of the same sulphuretted hydrogen water which had served for the experiments No. 86, and contained in 100 grammes - 02215 HS, were mixed with solution of cadmium in excess, filtered after 24 hours, and the precipitate washed, dried at 212 F., and weighed. Eesult, 0*2395. If the precipitate had consisted of pure sulphide of cadmium, it would have given, by calculation, 0-0247 per cent H S, consequently too much. A portion of it was therefore deflagrated with carbonate of soda and nitrate of potassa, and the residue tested for chlorine. Distinct re-action was observed. 96. CHLORIJIETRICAL EXPERIMENTS (to 224, sqq.) 10 grammes of chloride of, lime were triturated with water to one litre of fluid, with which the following experiments were made : a. Examination by Gay-Lussac's method ( 226) ; result, 23*42 23-52 per cent. b. Examination by Penofs method ( 227) ; result, 23-5 23-5 per cent. c. Examination by means of iron ( 228, modification a) ; result, 23-6 per cent. d. Examination by Bunsens method ( 228, D) ; result, 23-6 23'6 per cent 97. DRYING OF MANGANESE ORES (to 229, I.). Four small pans, I. TV., containing each 8 grammes of manganese ore of 53 per cent, were first dried in the water-bath. After 3 hours, I. had lost 0-145 ; after 6 hours, II. 0'15 ; after 9 hours, III. 0-15 ; after 12 hours, IV. 0'15 grm. I. and II. having been left standing, loosely covered, in the room for 12 hours, II. was found to weigh exactly as much as at first ; I. wanted only 0-01 grm. of the original weight. The four pans were now heated for 2 hours to 248 F. After cooling, they were found to have lost each 0'180 of the original weight. I. and II. having been left standing, loosely covered, in the room for 60 hours, were found to have again acquired their original weight by attracting moisture. III. and IV. were heated for 2 hours to 302 F. Both lost 0-215 grm. Having been left standing, loosely covered, in the room for 72 hours, both were found to weigh 0'05 less than at first. Assuming APPENDIX. 655 the hygroscopic moisture expelled to be re-absorbed by standing in the air, this shows that at 302 F. a little chemically combined water escapes along with the moisture, and, accordingly, that, in the drying of manganese ores, the temperature must not exceed 248 F. See also Dingler's " Polyt. Journ.," 135, 277 sqq. 98. COMPARATIVE DETERMINATIONS OF MANGANESE (to 230). A sample of manganese was dried at 212 F., and most carefully analysed, twice according to 230, A, and twice according to 230, C. The former method gave 61'33 and 61'42, the latter 6145 and 61-33 per cent. 99. DETERMINATION OP SILVER IN ARGENTIFEROUS LEAD [to 243, 1 (Production of the Bead), and 243, 1 (Determination of Silver in the Bead}, a]. a. 10 grammes of sulphide of lead and 0'3 grm. of sulphide of silver were treated as directed 243, 1, and the silver in the bead determined as directed 243, 1 (Determination of Silver in the Bead], a. Result, 8-093 grammes of bead, and from this, 0-3458 grm. of chloride of silver instead of 0-347 grm. b. 5 grammes of sulphide of lead and 0-05 grm. of sulphide of silver gave 4'025 grnis. of bead, and 0*0562 grm. of chloride of silver instead of 0-0578. c. 10 grammes of sulphide of lead and O'Ol grm. of sulphide of silver gave 7-7384 grms. of bead, and 0-0106 grm. of chloride of silver instead of 0-0115 grm. 100. VOLUMETRICAL DETERMINATION OF ZlNC BY SCHAFFNER'S METHOD (to 245, b, 2). An ammoniacal solution of 2-1081 grms. of oxide of zinc was prepared as directed 245, a, and diluted to 500 c.c. a. 50 c.c. of this solution, mixed first with 4, then with 2 additional drops of solution of sesquichloride of iron, required 25*3 c.c. of solution of sulphide of sodium. 6 drops of solution of sesquichloride of iron in 75 c.c. of ammoniated water, required 1-5 c.c. of solution of sulphide of sodium to produce a distinct color ; this leaves accordingly for the zinc solution, 25-3 1-5 = 23-8. b. 30 c.c., treated in the same way, required 15'3 (corrected). c. 25c.c. 13-1 According to a, 100 c.c. of zinc solution require 47 '6 c.c. of solution of sulphide of sodm. b, 510 11 Ai SJ 5J ) v-J T ) jj 656 APPENDIX. ADDENDUM. DETERMINATION OF ANTIMONY AND SEPARATION OF ARSENIC FROM ANTIMONY AND TIN. Bunsen (" Annal. d. Chem. u. Pharm.," 106, 3). a. DETERMINATION OF ANTIMONY. Bunsen recommends to weigh the antimony as antimonate of teroxide of antimony (Sb O 4 ), and gives two methods by which the conversion of tersulphide of antimony the form in which antimony is usually precipi- tated in analysis into antimonate of teroxide of antimony may be effected. a. Moisten the dry tersulphide of antimony with a few drops of nitric acid of 1*42 sp. gr., then treat, in a weighed porcelain crucible, with concave lid, with 8 10 times the quantity of fuming nitric acid,* and let the acid gradually evaporate on the water- bath. The sulphur separates at first as a fine powder, which, however, is readily and completely oxidized during the process of evaporation. The white residual mass in the crucible consists of antimonic acid and sulphuric acid, and may by ignition be converted, without loss, into antimonate of teroxide of anti- mony. If the tersulphide of antimony contains a large excess of free sulphur, this must first be removed by washing with bisulphide of carbon (see below), before proceeding to oxidation. /3. Mix the tersulphide of antimony with 30 50 times the quantity of pure oxide of mercury, t and heat the mixture gradually in an open porcelain crucible. As soon as oxidation begins, which may be known by the sudden evolution of gray mercurial fumes, moderate the heat. When the evolution of mercurial fumes diminishes, raise the temperature again, always taking care, however, that no inflammable reducing gases are brought into contact with the contents of the crucible. Eemove the last traces of oxide of mercury over the blast gas-lamp, then weigh the residual fine white powder of antimonate of teroxide of antimony. As oxide of mercury generally leaves a trifling fixed residue upon ignition, the amount of this should be determined once for all, the oxide of mercury added approximately weighed, and the corresponding amount of fixed residue deducted from the antimonate of teroxide of antimony. The volatilization of oxide of mercury proceeds much more rapidly when effected in a platinum crucible, instead of a porcelain one. But, if a platinum crucible is employed, it must be effectively protected from the action of antimony upon it, by a good lining of oxide of mercuryj. If * Nitric acid of 1 '42 sp. gr. is not suitable for their purpose, as its boiling point is almost 18 degrees Fahrenheit above the fusing point of sulphur, whereas fuming nitric acid boils at 186 '8 F., consequently below the fusing point of sulphur. With nitric acid of 1'42 sp. gr., therefore, the separated sulphur fuses and forms drops, which obstinately resist oxidation. f The best way is to use oxide of mercury prepared in the humid way ( 60, 4). + This is effected best, according to Bunsen, in the following way : Soften the sealed end of a common test-tube before the glass-blower's lamp ; place the softened end in the centre of the platinum crucible, and blow into it, which will cause it to expand and assume the exact form of the interior of the crucible. Crack off the bottom of the glass and smooth the sharp edge cautiously by fusion. A glass is thus obtained, open at both ends, which exactly fits the crucible. To effect the lining by means of this instrument, fill the crucible loosely with oxide of mercury up to the brim, then force the glass gradually and slowly down to the bottom of the crucible, occasionally shaking out the APPENDIX. 657 the tersulphide of antimony contains free sulphur, this must first be removed by washing with bisulphide of carbon, before the oxidation can be pro- ceeded with, since otherwise a slight deflagration is unavoidable. The bisulphide of carbon used may be very easily rectified, and then used again, so that the washing of a precipitate may be effected with as little as 10 15 grammes of bisulphide of carbon. b. SEPARATION OF ARSENIC FROM ANTIMONY AND TIN. This new method is based upon the different deportment of the recently precipitated sulphides of these metals with bisulphite of potassa. If re- cently precipitated tersulphide of arsenic is digested with sulphurous acid and bisulphite of potassa, the precipitate is dissolved; upon boiling, the fluid becomes turbid, owing to the separation of sulphur, of which the greater part, however, disappears upon continued boiling. After the expulsion of the sulphurous acid, the fluid contains arsenite and hyposulphite of potassa [2 As S 3 + 8 (K O, 2 S0 a ) = 2 (K O, As O 3 ) + 6 (K O, S a O 2 ) + S 3 + 7 S O J. Tersulphide of antimony and sulphide of tin do not show this re-action. They may, accordingly, both be separated from tersulphide of arsenic, simply by precipitating the solution of the three sulphides in sulphide of,' potassium, with a large excess of a solution of sulphurous acid in water, digesting the fluid for some time with the precipitate on the water-bath, and then boiling until about two-thirds of the water and the whole of the sulphurous acid are expelled. The residual tersulphide of antimony and sulphide of tin is free from arsenic, the filtrate containing the whole of the arsenic, which may be precipitated at once with sulphuretted hydrogen. To determine the arsenic, Bunsen oxidizes the dry tersul- phide of arsenic, together with the filter, wiih fuming nitric acid, gently heats the slightly diluted solution with a little chlorate of potassa (to ensure the complete oxidation of the substances derived from the paper), and determines the arsenic finally as arsenate of magnesia and ammonia. In separating the sulphide of tin from the solution of arsenite of potassa, care must be taken to wash the sulphide of tin with concentrated solution of chloride of sodium, as the fluid runs turbid through the filter if pure water is used. As soon as the precipitate has been thoroughly washed with solution of chloride of sodium, the chloride of sodium adhering to the precipitate is removed by washing with a sohition of acetate of ammonia containing a slight excess of acetic acid. The washings proceed- ing from this last operation must not be added to the chloride of sodium washings, as acetate of ammonia prevents the complete precipitation of arsenious acid by sulphuretted hydrogen. Bunsen obtained very satisfactory results by this method. oxide of mercury from the interior of the glass. The inside of the crucible is thus covered with a layer of oxide of mercury $ 1 line thick, which, after the removal of the glass, adheres with sufficient firmness, even upon ignition. 658 APPENDIX. II. TABLES FOR THE CALCULATION OF ANALYSES. TABLE I. EQUIVALENTS OF THE ELEMENTS CONSIDERED IN THE PRESENT WORK.* Aluminium Antimony Arsenic Barium Bismuth Boron Bromine Cadmium Calcium Carbon Chlorine Chromium Cobalt Copper Fluorine Gold Hydrogen Iodine Iron Lead Lithium Magnesium Manganese Mercury Molybdenum Al Sb As Ba Bi B Br Cd Ca Cl Cr Co Cu Fl Au H I Fe Pb Li Mg Mn Hg Mo = 100. 170-42 1503-80 937-50 857-32 2599-95 138-05 999-62 700-00 250-00 75-00 443-28 328-00 375-00 396-00 237-50 2458-33 12-50 1586-00 350-00 1294-65 86-89 150-19 344-68 1250-60 575-00 11 = 1. 13-63 120-30 75-00 68-59 208-00 11-04 79-97 j 56-00 20-00 j 6-00 35-46 j 26-241) 30-00 31-68 19-00 196-67 1-00 126-88 j 28-00 103-57 6-95 12-00 27-57 100-05 46-00 (Berzelius) (Schneidert) (Pelouze, Berzelius) (Marignac) (Schneider) (Berzelius) (Marignac, revised by Ber- zelius) (C. v. Hauerl) (Dumas ; Erdmann and Marchand) ,, (Marignac, revised byBer- zelius) (Berlin, Peligot) (Schneider) (Erdmann & Marchand) (Louyet) (Berzelius) (Dumas) ( Mari S nac > revised byBer- (Erdmann & Marchand) (Berzelius) (Mallet) (Marchand & Scheerer) (Berzelius) (Erdmann & Marchand) (Berlin) * These equivalent numbers are derived from most careful and accurate investigations. Several of them differ from the numbers originally assumed, though not in consequence of recent direct experiments, but simply because they were originally derived from other equivalents which have since been corrected by more accurate investigations. It became necessary, therefore, to adjust the equivalents derived from the original numbers to the corrected numbers. For a detailed and very instructive statement of the various sources from which our present knowledge of the equivalents of the elements, &c., is derived, I refer to A . Strecker's paper on Atomic Weights in ' ' Handworterbuch der reinen u. angewandten Chemie," 2nd edit., vol. 2, 463. f "Pogg. Annal.," 98, 293. Schneider's first experiments (" Journ. f. prakt. Chem., 68, 117) had given 1503, or 120 '2, the numbers which I have still retained in 90. J "Reports of Sittings of the Academy of Sciences at Vienna," XXV., 118. I did not receive this most carefully determined equivalent number of cadmium in time to make use of it in the body of the present work. The old number (Stromeyer's), viz., 696 - 77, or 55-74, has accordingly been used in 87. || In 76, I have still retained the old equivalent of chromium, as determined by Mobercj, Lefort, and Wildenatein, viz., 334 '7, or 26 '78. The number given in the table (328 "00, or 26 "24), which results from Berlin's corrections of LeforCa experiments ("Journ. f. prakt. Chem.," 71, 191), deserves, however, the preference. Nickel Ni Nitrogen N Oxygen Palladium Pd Phosphorus Platinum P Pt Potassium K Selenium Se Silicon Si Silver Ag Sodium Na Strontium Sr Sulphur S Tin Sn Titanium Ti Uranium Ur Zinc Zn APPENDIX. = 100. 362-50 175-06 100-00 665-48 387-50 1236-75 659 29-00 (Schneider) 14-00 | ( Mari 8 nac revised by Ber- 8-00 53-24 (Berzelius) 31-00 (Schrotter) 98-94 (Andrews) 39-11 j 185-18* 1349-66 287-44 545-93 200-00 725-00 312-50 742-87 406-59 _ Q _ J" (Berzelius, Sacc, Erdmann * \ & Marchand mean) 14-81 (Berzelius) 107 . 97 j (Marignac, revised by Ber- 23 -00- (Pelouze) 43-67 (Stromeyer) 16-00 (Erdmann & Marchand) 58-00 (Mulder) 25-00 (Pierre) 59-40 (Ebelmen) 32-53 (Axel Erdmann) * 185-18 is two-thirds of the number given by JSerzelius, viz., 277 '778, as I have regarded silicic acid as Si O s . u u 2 660 APPENDIX. TABLE II. COMPOSITION OF THE BASES AND OXYGEN ACIDS. a. BASES. GROUP I. Potassa K . . O . . . 488-86 . . 100-00 . 39-11 . 8-00 . 83-02 16-98 KO . . 588-86 . 47-11 . 100-00 Soda Na . . O . . . 287-44 . . 100-00 . 23-00 . 8-00 . 74-19 25-81 NaO . . 387-44 . 31-00 . 100-00 Lithia Li . . O . . . 86-89 . . 100-00 . 6-95 . 8-00 . 46-49 53-51 LiO . . 186-89 . 14-95 . 100-00 Oxide of Ammonium NH 4 . . . . 225-06 . . 100-00 . 18-00 . 8-00 . 69-23 30-77 NH 4 . 325-06 . 26-00 . 10Q-00 GROUP II. Baryta Ba . . O . . . 857'32 . . 100-00 . 68-59 . 8-00 . 89-55 10-45 BaO . . 957-32 . 76-59 . 100-00 Strontia Sr . . O . . . 545-93 . . 100-00 . 43-67 . 8-00 . 84-52 15-48 SrO . . 645-93 . 51-67 . 100-00 Lime Ca . . O . . . 250-00 . . 100-00 . 20-00 . 8-00 . 71-43 28-57 CaO . . 350-00 . 28-00 . 100-00 Magnesia Mg O . . . 15019 . . 100-00 . 12-00 . 8-00 . 60-03 39-97 MgO . . 250-19 . 20-00 . 100-00 GROUP III. Alumina A1 2 . . 3 , . 340-84 . . 300-00 . 27-26 . 24-00 . 5319 46-81 A1 2 3 . . 640-84 . 51-26 . 100-00 APPENDIX. 661 GEOUP III. Chromium, sesquioxide Cr 2 . . . 656'00 . 52'4S . 68-62 O 3 . . . 300-00 . 24-00 . 31-38 Cr 2 3 . . 956-00 . 76-48 . 100-00 GEOUP IV. Zinc, oxide Zn . . . . . 406-59 . 100-00 . 32-53 . . 8-00 . 80-26 19-74 ZnO . . 506-59 . 40-53 . 100-00 Manganese, protoxide Mn . O . . . 344-68 . 100-00 . 27-57 . . 8-00 . 77-51 22-49 MnO . . 444-68 . 35-57 . 100-00 ... > Manganese, sesquioxide Mn, . 3 . . 689-36 . 300'00 . 55-14 . . 24-00 . 69-67 30-33 MnA. . 989-36 . 79-14 . 100-00 Nickel, protoxide Ni . . . . . 362-50 . 100-00 . 29-00 . . 8-00 . 78-38 21-62 NiO . . 462-50 . 37-00 . ] 00-00 Cobalt, protoxide Co . . O . . . 375-00 . 100-00 . 30-00 . . 8-00 . 78-95 21-05 CoO . . 475-00 ; 38-00 . 100-00 Cobalt, sesquioxide Co a . 3 . . . 750-00 . 300-00 . 60-00 . . 24-00 . 71-43 28-57 Co 2 3 . . 1050-00 . 84-00 . 100-00 Iron, protoxide Fe . . . . . 350-00 . 100-00 . 28-00 . . 8-00 . 77-78 22-22 FeO . . 450-00 . 36-00 . 100-00 Iron, sesquioxide Fe 2 . . . 700-00 . 300-00 . 56-00 . . 24-00 . 70-00 30-00 Fe 2 3 . . 1000-00 . 80-00 . 100-00 GEOUP V. . Silver, oxide Ag O . . . 1349-66 . 100-00 . 107-97 . . 8-00 . 93-10 6-90 AgO . . 1449-66 . 115-97 . 100-00 Lead, oxide Pb O . . . 1294-65 . 100-00 . 103-57 . . 8-00 . 92-83 7-17 PbO . . 1394-65 . 111-57 . 100-00 Mercury, suboxide H g2 . O . . . 2501-20 . 100-00 . 200-10 .. . 8-00 . 96-16 3-84 Hg 2 . . 2601-20 . 208-10 . 100-00 662 APPENDIX. Mercury, oxide Copper, suboxide Copper, oxide Bismuth, oxide Cadmium, oxide GKOUP VI. Gold, teroxide Platinum, binoxide Antimony, teroxide Tin, protoxide Tin, binoxide Arsenious Acid Hg . . 1250-60 . 100-05 . 92-59 . . . 100-00 . 8-00 7-41 HgO . 1350-60 . 108-05 . 100-00 Cu, . . 792-00 . 63-36 ; 88-79 . . . 100-00 . 8-00 . 11-21 C^O . 892-00 . 71-36 . 100-00 Cu . . 396-00 . 31-68 . 79-84 O . . . 100-00 . 8-00 . 20-16 CuO . . 496-00 . 39-68 . 100-00 Bi . 2599-95 . 208-00 . 89-655 O 3 . 300-00 . 24-00 . 10-345 Bi0 3 . 2899-95 . 232-00 . 100-000 Cd . . . 700-00 . 56-00 . 87-50 . . . 100-00 . 8-00 . 12-50 CdO . . 800-00 . 64-00 . 100-00 'Au . . . 2458-33 . 196-67 . 89-12 3 . . . 300-00 . 24-00 . 10-88 Au0 3 . . 2758-33 . 220-67 . 100-00 Pt . . . 1236-75 . 98-94 . 86-08 2 . . . 200-00 . 16-00 . 13-92 PtO 2 . . 1436-75 . 114-94 . 100-00 Sb . . . 1503-80 . 120-30 . 83-37 3 . . 300-00 . 24-00 . 16-63 Sb0 3 . . 1803-80 . 144-30 . 100-00 Sn . . . 725-00 . 58-00 . 87-88 O .. . . 100-00 . 8-00 . 12-12 SnO . . 825-00 . 66-00 . 100-00 Sn . . . 725-00 . 58-00 . 78-38 2 . . . 200-00 . 16-00 . 21-62 SnO 2 . . 925-00 . 74-00 . 100-00 As . . . 937-50 . 75-00 . 75-76 3 . . . 300-00 . 24-00 . 24-24 As0 3 . 1237-50 . 99-00 . 100-00 APPENDIX. 663 GROUP VI. Arsenic acid Chromic acid Sulphuric acid Phosphoric acid Boracic acid Oxalic acid Carbonic acid Silicic acid Nitric acid Chloric acid As . . 5 . . . 937-50 . 500-00 . 75-00 . 40-00 . 65-22 . 34-78 AsO s . ACIDS. Cr . . 8 . . . 1437-50 . 328-00 . 300-00 . 115-00 . 26-24 . 24-00 . 100-00 . 5223 . 47-77 Cr0 3 . S . . 3 . . . 628-00 . 200-00 . 300-00 . 50-24 . 16-00 . 24-00 . 100-00 . 40-00 . 60-00 S0 3 . p . . o s . . . 500-00 . 387-50 . 500-00 . 40-00 . 31-00 . 40-00 . 10000 . 43-66 . 56-34 P0 6 - B . . 3 . . 887-50 . 138-05 . 300-00 . 71-00 . 11-04 . 24-00 . 100-00 . 31-51 . 68-49 B0 3 . C 2 . . 3 . . . 438-05 . 150-00 . 300-00 . 35-04 . 12-00 . 24-00 . 100-00 . 33-33 . 66-67 CA . c . . 2 . . . 450-00 . 75-00 . 200-00 . 36-00 . 6-00 . 16-00 . 10000 . 27-27 . 72-73 CO, . Si . . 2 . . . 275-00 . 185-18 . 200-00 . 22-00 . 14-81 . 1600 . lOp-00 . 48-08 . 51-92 Si0 2 . N . . o... . . 385-18 . 175-06 . 500-00 30-81 t . 14-00 . 40-00 . 100-00 . 25-93 . 74-07 NO S . Cl . . o 5 . . . 675-06 . 443-28 . 500-00 . 54-00 . 35-46 . 40-00 . 100-00 . 46-99 . 53-01 C10 S . . 943-28 . 75-46 . 100-00 APPENDIX. TABLE III. FOR CALCULATING THE EQUIVALENT OF ONE OF THE CONSTITUENTS BY SIMPLE MULTIPLICATION OR DIVISION OF THE EQUIVALENT OF THE COMPOUND. This Table contains only some of the more frequently occurring com- pounds ; the formulae preceded by ! give perfectly accurate results. The Table may also be extended to other compounds, by proceeding accord- ing to the instructions given in 199. FOR INORGANIC ANALYSIS. CARBONIC ACID. ! Carbonate of lime x 0'4:4;=Carbonic acid. CHLORINE. Chloride of silver xO-24724=Chlorine. COPPER. Oxide of copper xO*79839=Copper. IRON. ! Sesquioxide of iron x 0*7=2 Iron. ! Sesquioxide of ironxO'9=2 Protoxide of iron. LEAD. Oxide of lead xO*92S3=Lead. Pyropkosphate of magnesia x 0*36036=2 Magnesia. MANGANESE. Protosesquioxide of manganese x 0*72107=3 Manganese. Protosesquioxide of manganese x 0*9303 =3 Protoxide of manganese. PHOSPHORIC ACID. Pyrophosphate of magnesia x 0*6396=Phosphoric acid. Phosphate of sesquioxide of uranium (2 Ur 2 3 P0 5 ) X 0*2 \ Phosphate of sesquioxide of uranium [ =Phosphoric acid . 5 POTASSA. Chloride of potassium xO*52"145=Potassium. Sulphate of potassaxO*5408=Potassa. Potassio-bichloride of platinum x 0*30507^ Potassio-bichloride of platinum [ =Chloride of potassium. 3-278 J APPENDIX. 665 Potassio-bichloride of platinum x 019272 1 . Potassio-bichloride of platinum f =Potassa. 5188 ) SODA. Chloride of sodium xO'5302=Soda. Sulphate of sodaxO'43658=Soda. SULPHUR. Sulphate of baryta x013724=Sulphur. SULPHURIC ACID. Sulphate of baryta xO'34309=Sulphuric acid. FOR ORGANIC ANALYSIS. CARBON. Carbonic acid x 0'2727 or Carbonic acid 3-666 or ! Carbonic acid x 3 n Water x 0-1111 or ! Water = Hydrogen. NITROGEN. Ainmonio-bichloride of platinum xO'06271=Nitrogen. Platinum x 0'1415 ^Nitrogen. 666 APPENDIX. TABLE Showing the AMOUNT OF THE NUMBER OF THE COMPOUND Elements. Found. Sought. 1 Aluminium Alumina Aluminium 0-53186 Ammonium Chloride of ammonium Ammonia 0-31804 N H 4 C1 NH 3 Ammonio-bichloride of platinum Oxide of ammonium 0-11644 NH 4 Cl,PtCl 2 Ammonio-bichloride of platinum N H 4 , Ammonia 0-07614 Antimony NH.ClPtCL, Teroxide of antimony NH, Antimony 0-83368 SbO, Tersulphide or antimony Sb Antimony 0-71479 SbS 3 Tersulphide of antimony Sb Teroxide of antimony 0-85740 SbS 3 Sb0 3 Antimonious acid Teroxide of antimony 0-94747 Sb0 4 Sb0 3 Arsenic Arsenious acid Arsenic 0-75758 AsO 3 As Arsenic acid Arsenic 0-65217 AsO As Arsenic acid Arseuious acid 0-86087 As0 5 As0 3 Tersulphide of arsenic Arsenious acid 0-80488 AsS 3 AsO 3 Tersulphide of arsenic Arsenic acid 0-93496 AsS 3 AsO 5 Arsenate of ammonia and magnesia 2MgO,NH 4 0,As0 6 + aq Arsenate of ammonia and magnesia Arsenic acid As0 5 Arsenious acid 0-60526 0-52105 Barium 2MgO,NH 4 0,AsO 6 + aq Baryta AsO 3 Barium 0-89554 BaO Ba Sulphate of baryta Baryta 0-65690 Ba O, S O 3 BaO Carbonate of baryta Baryta 0-77684 Ba O, C O. Silico-fluoride of barium BaO Baryta 0-54548 Bismuth BaFl,SiFl 2 Teroxide of bismuth BaO Bismuth 0-89655 Bi0 3 Bi Boron Boracic acid Boron 0-31515 Bromine BO 3 ' Bromide of silver B Bromine 0-42550 Cadmium AgBr Oxide of cadmium Br Cadmium 0-87500 CdO Cd Calcium Lime Calcium 0-71429 CaO Ca Sulphate of lime Lime 0-41176 CaO,S0 3 CaO APPENDIX. IV. CONSTITUENT SOUGHT for every FOUND, from 1 9. 2 3 4 5 6 7 8 9 1-06373 1-59559 2-12746 2-65932 3-19118 3-72305 4-25491 4-78678 0-63608 0-95413 1-27217 1-59021 1-90825 2-22629 2-54433 2-86237 0-23288 0-34932 0-46576 0-58220 0-69864 0-81508 0-93152 1-04796 0-15228 0-22842 0-30456 0-38070 0-45684 0-53299 0-60913 0-68527 1-66736 2-50104 3-33472 4-16840 5-00208 5-83576 6-66944 7-50312 1-42959 2-14438 2-85918 3-57397 4-28877 5-00356 5-71836 6-43315 1-71480 2-57219 3-42959 4-28699 5-14439 6-00179 6-85918 7-71658 1-89494 2-84242 3-78989 4-73736 5-68483 6-63230 7-57978 8-52725 > 1-51516 2 27274 3-03032 3-78790 4-54548 5-30306 6-06064 6-81822 1-30435 1-95652 2-60870 3-26087 3-91304 4-56522 5-21739 5-86957 1-72174 2-58261 3-44348 4-30435 516521 6-02608 6-88695 7-74782 1-60975 2-41463 3-21951 4-02439 4-82927 5-63415 6-43902 7-24390 1-86992 2-80488 3-73984 4-67480 5-60975 6-54471 7-47967 8-41463 1-21053 1-81579 2-42105 3-02631 3-63158 4-23684 4-84210 5-44737 1-04210 1-56316 2-08421 2-60526 3-12631 3-64736 4-16842 4-68947 1-79108 2-68662 3-58216 4-47770 5-37325 6-26879 7-16433 8-05987 1-31380 1-97070 2-62760 3-28450 3-94140 4-59830 5-25520 5-91210 1-55369 2-33053 3-10737 3-88421 4-66106 5-43790 6-21474 6-99158 1-09096 1-63644 2-18192 2-72740 3-27288 3-81836 4-36384 4-90932 1-79310 2-68965 3-58620 4-48275 5-37930 6-27586 7-17240 8-06895 0-63029 0-94544 1-26058 1-57573 1-89088 2-20602 2-52117 2-83631 0-85100 1-27650 1-70200 2-12750 2-55300 2-97850 3-40400 3-82950 1-75000 2-62500' 3-50000 4-37500 5-25000 6-12500 7-00000 7-87500 1-42857 2-14286 2-85714 3-57143 4-28571 5-00000 5-71429 6-42857 0-82353 1-23529 1-64706 2-05882 2-47059 2-88235 3-29412 3-70588 668 APPENDIX. TABLE IV. Elements. Found. Sought. 1 Calcium Carbonate of lime Lime 0-56000 Carbon CaO,C0 2 Carbonic acid CaO Carbon 0-27273 C0 2 C Carbonate of lime Carbonic acid 0-44000 Chlorine CaO,C0 2 Chloride of silver CO., Chlorine 0-24724 AgCl Cl Chloride of silver Hydrochloric acid 0-25421 AgCl HC1 Chromium Sesquioxide of chromium Chromium 0-68619 Cr 2 3 Cr 2 Sesquioxide of chromium Chromic acid 1-31381 Cr 2 3 2CrO 3 Chromate of lead Chromic acid 0-31049 Cobalt PbO,Cr0 3 Cobalt Cr0 3 ' Protoxide of cobalt 1-26667 Co CoO Sulphate of protoxide of cobalt Protoxide of cobalt 0-48718 CoO, SO 3 CoO Copper Oxide of copper CuO Cogper 0-79839 Fluorine Subsulphide of copper Cu^S Fluoride of calcium Copper Fluorine 0-79839 48718 CaFl Fl Fluoride of silicon Fluorine 0-71950 SiFl 2 2F1 Hydrogen Water Hydrogen 0-11111 HO H Iodine Iodide of silver Iodine 0-54025 Agl I Iodide of palladium Iodine 0-70443 Pdl I Iron Sesquioxide of iron Iron 0-70000 Fe ? 3 Fe 2 Sesquioxide of iron Protoxide of iron 0-90000 Lead Oxide of lead 2FeO Lead 0-92830 PbO Pb Sulphate of lead Oxide of lead 0-73609 PbO,S0 3 PbO Chloride of lead Oxide of lead 80248 PbCl PbO Chloride of lead Lead 0-74494 PbCl Pb Sulphide of lead Oxide of lead 93309 PbS PbO Magnesium Ma^gia Magnesium Mg 0-60030 Sulphate of magnesia MgO,SO 3 Magnesia MgO 0-33350 Pyrophosphate of magnesia 2MgO,PO, Magnesia 2 MgO 0-36036 APPENDIX. (continued). 2 3 4 5 6 7 8 9 1-12000 1-68000 2-24000 2-80000 3-36000 3-92000 4-48000 5-04000 0-54546 0-81818 1-09091 1-36364 1-63636 1-90909 2-18181 2-45455 0-88000 1-32000 1-76000 2-20000 2-64000 3-08000 3-52000 3-96000 0-49448 0-74172 0-98896 1-23620 1-48344 1-73068 1-97792 2-22516 D-50842 0-76263 1-01684 1-27105 1-52526 1-77947 2-03368 2-28789 1-37238 2-05858 2-74477 3-43096 4-11715 4-80334 5-48954 6-17573 2-62762 3-94142 5-25523 6-56904 7-88285 9-19666 10-51046 11-82427 0-62097 0-93146 1-24195 1-55244 1-86293 2-17341 2-48390 2-79439 2-53333 3-80000 5-06666 6-33333 7-60000 8-86666 10-13333 11-39999 0-97436 1-46154 1-94872 2-43590 2-92308 3-41026 3-89744 4-38462 1-59677 2-39516 3-19355 3-99193 4-79032 5-58871 6-38710 7-18548 1-59677 2-39516 3-19355 3-99193 4-79032 5-58871 6-38710 7-18548 0-97436 1-46154 1-94872 2-43590 2-92307 3-41027 3-89743 4-38461 1-43900 2-15850 2-87800 3-59750 4-31700 5-03650 5-75600 6-47550 0-22222 0-33333 0-44444 0-55555 0-66667 0-77778 0-88889 1-00000 1-08050 1-62075 2-16100 2-70125 3-24150 3-78175 4-32200 4-86225 1-40886 2-11329 2-81772 3-52215 4-22658 4-93101 5-63544 6-33987 1-40000 2-10000 2-80000 3-50000 4-20000 4-90000 5-60000 6-30000 1-80000 2-70000 3-60000 4-50000 5-40000 6-30000 7-20000 8-10000 1-85660 2-78490 3-71320 4-64150 5-56980 6-49810 7-42640 8-35470 1-47219 2-20829 2-94438 3-68048 4-41658 5-15268 5-88878 6-62487 1-60495 2-40743 3-20990 4-01238 4-81486 5-61734 6-41982 7-22229 1-48987 2-23480 2-97974 3-72468 4-46962 5-21455 5-95949 6-70442 1-86619 2-79928 3-73238 4-66547 5-59856 6-53166 7-46475 8-39785 1-20061 1-80091 2-40121 3-00151 3-60182 4-20212 4-80242 5-40273 0-66700 1-00051 1-33401 1-66751 2-00101 2-33451 2-66802 3-00152 0-72072 1-08108 1-44144 1-80180 2-16216 2-52252 2-88288 3-24324 670 APPENDIX. TABLE IV. Elements. Found. Sought. 1 Manganese Protoxide of manganese Manganese 0-77512 MnO Mu Protosesquioxide of manganese Manganese 0-72105 MnO + Mn 2 3 Sesquioxide of manganese Mn2O 3 Mn 3 Manganese Mn 2 0-69678 Sulphate of protoxide of manganese MnO,S0 3 Protoxide of manganese MnO 0-47072 Mercury Mercury Suboxide of mercury 1-0399S Hg 2 Hg 2 Mercury Oxide of mercury 1-07996 Hg HgO Subchloride of mercury Mercury 0-84945 Hg 2 Cl JJg Sulphide of mercury Mercury 0-86213 Nickel HgS Protoxide of nickel Nickel 0-78378 NiO Ni Nitrogen Aminonio-bichloride of platinum Nitrogen 0-06071 N H 4 Cl, Pt CL, Platinum Pt N Nitrogen 0-14155* Sulphate of baryta Nitric acid 0-46322 BaO,SO 3 Cyanide of silver Ag,C 2 N Cyanide of silver Ag,C 2 N N0 6 Cyanogen "C 2 N Hydrocyanic acid C 2 N,H 0-19410 0-20156 Oxygen Alumina Oxygen 0-46814 A1 2 3 O 3 Teroxide of antimony Oxygen 0-16632 Sb0 3 3 Arsenious acid Oxygen 0-24242 AsO 3 4 Arsenic acid Oxygen 0-34783 As0 5 O s Baryta BaO Oxygen 0-10446 Oxide of lead Oxygen 0-07170 PbO Oxide of cadmium Oxygen 0-12500 CdO Lime Oxygen 0-28571 CaO Sesquioxide of chromium Oxygen 0-31381 Cr 2 3 3 Sesquioxide of iron Oxygen 0-30000 Fe ? 3 Protoxide of iron 3 Oxygen 0-22222 FeO Potassa Oxygen 0-169S2 KO O Silicic acid Oxygen 0-5192b SiOj 6 2 APPENDIX. (continued). 2 3 4 5 6 7 8 9 1-55024 2-32536 3-10048 3-87560 4-65072 5-42584 6-20096 6-97608 1-44214 2-16321 2-88428 3-60535 4-32641 5-04748 5-76855 6-48962 1-39356 2-09034 2-78712 3-48390 4-18068 4-87746 5-57424 6-27102 0-94144 1-41217 1-88289 2-35361 2-82433 3-29505 3-76578 4-23650 2-07996 3-11994 4-15992 5-19990 6-23988 7-27986 8-31984 9-35982 2-15992 3-23988 4-31984 5-39980 6-47977 7-55973 8-63969 9-71965 1-69890 2-54836 3-39781 4-24726 5-09672 5-94617 6-79562 7-64508 172425 2-58638 3-44850 4-31063 5-17275 6-03488 6-89701 7-75913 1'56757 2-35135 3-13514 3-91892 4-70270 5-48649 6-27027 7-05406 0-12542 0-18812 0-25083 0-31354 0-37625 0-43896 0-50166 0-56437 0-28310 0-42464 0-56619 0-70774 0-84929 0-99084 1-13238 1-27393 0-92644 ] -38966 1-85288 2-31610 2-77932 3-24254 3-70576 4-16898 0-38820 0-58230 0-77640 0-97050 1-16460 1-35870 1-55280 1-74690 0-40312 0-60468 0-80624 1-00780 1-2093.6 1-41092 1-61248 1-81404 0-93627 1-40441 1-87254 2-34068 2-80882 3-27695 3-74509 4-21322 0-33264 0-49896 0-66528 0-83160 0-99792 1-16424 1-33056 1-49688 0-48484 0-72726 0-96968 1-21210 1-45452 1-69694 1-93936 2-18178 0-69565 1-04348 1-39] 30 1-73913 2-08696 2-43478 2-78261 3-13043 0-20892 0-31338 0-41784 0-52230 0-62675 0-73121 0-83567 0-94013 0-14340 0-21510 0-28680 0-35850 0-43020 0-50190 0-57360 0-64530 0-25000 0-37500 0-50000 0-62500 0-75000 0-87500 1-00000 1-12500 0-57143 0-85714 1-14286 1-42857 1-71429 2-00000 2-28571 1-57143 0-62762 0-94143 1-25524 1-56905 1-88286 2-19667 2-51048 2-82429 0-60000 0-90000 1-20000 1-50000 1-80000 2-10000 2-40000 2-70000 0-44444 0-66667 0-88889 1-11111 1-33333 1-55555 1-77777 1-99999 0-33964 0-50946 0-67928 0-84910 1-01892 1-18874 1-35856 1-52838 1-03846 1-55769 2-07692 2-59615 3-11538 3-63461 4-15384 4-67307 672 APPENDIX. TABLE IY. Elements. Found. Sought. 1 Oxygen Protoxide of cobalt CoO Oxygen 0-21053 Oxide of copper CuO Oxygen 0-20161 Magnesia Oxygen 0-39970 Protoxide of manganese b Oxygen 0-22488 MnO O Protosesquioxide of manganese Oxygen 0-27893 MnO + Mn 2 3 Sesquioxide of manganese Oxygen 0-30322 Mn 2 3 o, Soda Oxygen 0-25S10 NaO b Protoxide of nickel Oxygen 0-21622 NiO O Oxide of mercury Oxygen 0-07404 HgO O Suboxide of mercury Oxygen 0-03844 Hg 2 Oxide of silver O Oxygen 0-06898 AgO Strontia Oxygen 0-15482 SrO b Water Oxygen 0-88889 HO b Teroxide of bismuth BiO 3 Oxygen 0-18345 9 Oxide of zinc ZnO Oxygen 0-19740 Binoxide of tin Oxygen 0-21622 Phosphorus Sn0 2 Phosphoric acid PO 5 2 Phosphorus 0-43662 Pyrophosphate of magnesia Phosphoric acid 0-63964 2 Mg O, P O 5 Phosphate of sesquioxide of iron Phosphoric acid 0-47020 Fe-O^POs P0 5 Phosphate of silver Phosphoric acid 0-16949 3AgO,PO, Pyrophosphate of silver Phosphoric acid 0-23437 2AgO,PO 5 P O. Potassium Potassa Potassium 0-83018 KO K Sulphate of potassa Potassa 0-54080 KO,S0 3 KO Nitral e of potassa Potassa 0-46590 KO.NO, KO Chloride of potassium Potassium 0-52445 KC1 K Chloride of potassium Potassa 0-63173 KC1 KO Potassio-bichloride of platinum Potassa 0-19272 KCl,PtCl 2 KO APPENDIX. 673 (continued!). 2 3 4 5 6 7 8 9 0-42106 0-63159 0-84212 1-05265 1-26318 1-47371 1-68424 1-89477 0-40323 0-60484 0-80645 1-00807 1-20968 1-41129 1-61290 1-81452 0-79939 1-19909 1-59879 1-99849 2-39818 2-79788 3-19758 3-59727 0-44976 0-67464 0-89952 1-12440 1-34928 1-57416 1-79904 2-02392 0-55786 0-83679 1-11572 1-39465 1-67359 1-95252 2-23145 2-51038 0-60644 0-90966 1-21288 1-51610 1-81932 2-12254 2-42576 2-72898 0-51621 0-7743] 1-03242 1-29052 1-54863 1-80673 2-06484 2-32294 0-43244 0-64866 0-86488 1-08110 1-29732 1-51354 1-72976 1-94598 0-14808 0-22212 0-29616 0-37021 0-44425 0-51829 0-59233 0-66637 0-07688 0-11533 0-15377 0-19221 0-23066 0-26910 0-30754 0-34599 '0-13796 0-20694 0-27592 0-34490 0-41388 0-48286 0-55184 0-62082 . 0-30964 0-46446 0-61928 0-77410 0-92892 1-08374 1-23856 1-39338 1-77778 2-66667 3-55556 4-44445 5-33333 6-22222 7-11111 8-00000 0-20690 0-31035 0-41380 0-51725 0-62070 0-72415 0-82760 0-93105 0-39480 0-59220 0-78960 0-98700 1-18440 1-38180 1-57920 1-77660 0-43244 0-64866 0-86488 1-08110 1-29732 1-51354 1-72976 1-94598 0-87324 1-30896 1-74648 2-18309 2-61971 3-05633 3-49295 3-92957 1-27928 1-91982 2-55856 3-19820 3-83784 4-47748 5-11712 5-75676 0-94040 1-41060 1-88080 2-35099 2-82119 3-29139 3-76159 4-23179 0-33898 0-50847 0-67796 0-84745 1-01694 1-18643 1-35592 1-52541 0-46874 0-70311 0-93748 1-17185 1-40622 1-64059 1-87496 2-10933 1-66036 2-49054 3-32072 4-15090 4-98108 5-81126 6-64144 7-47162 1-08161 1-62241 2-16321 2-70402 3-24482 3-78563 4-32643 4-86723 0-93179 1-39769 1-86359 2-32949 2-79539 3-26129 3-72719 4-19309 1-04890 1-57335 2-09780 2-62225 3-14669 3-67114 4-19559 4-72004 1-26346 1-89519 2-52692 3-15865 3-79037 4-42210 5-05383 5-68556 0-38545 0-57817 0-77090 0-96362 1-15634 1-34907 1-54179 1-73452 II. X X 674 APPENDIX. TABLE IY. Elements. Found. Sought. 1 Potassium Potassio-bichloride of platinum Chloride of potassium 0-30507 K Cl, Pt CL KC1 Silicon Silicic acid Silicon 0-48077 SiO Si Silver Chloride ot ? silver Silver 0-75276 AgCl A ? Chloride of silver Oxide ol silver 0-SOS54 AgCl A^O Sodium Soda Sodium 0-74190 NaO Na Sulphate of soda Soda 0-43658 NaO, SO 3 NaO Nitrate of soda Soda 0-36465 NaO,N0 5 NaO Chloride of sodium Soda 0-53022 Nad NaO Chloride of sodium Sodium 039337 Nad Na Carbonate of soda Soda 0-584S7 Strontium NaO,C0 2 Strontia " NaO Strontium 0-84518 SrO Sr Sulphate of strontia Strontia 0-56367 Sr 0, S O 3 SrO Carbonate of strontia Strontia 0-70139 SrO,CO 2 SrO Sulphur Sulphate of baryta Sulphur 0-13724 BaO,SO 3 S Tersulphide of arsenic Sulphur 0-39024 AsS 3 83 Sulphate of baryta BaO,S0 3 Sulphuric acid SO, 0-34309 Tin Binoxide of tin Tin 0-78378 Sn0 2 Sn Binoxide of tin Protoxide of tin 0-S9189 Sn0 2 SnO Zinc Oxide of zinc Zinc 0-80260 ZnO Zn (continued). APPENDIX. 2 3 4 5 6 7 8 9 0-61015 0-91522 1-22030 1-52537 1-83044 2-13552 2-44059 2-74567 0-96154 1-44231 1-92308 2-40385 2-88462 3-36539 3-84616 4-32693 1-50552 2-25828 3-01104 3-76380 4-51656 5-26932 6-02208 6-77484 1-61708 2-42562 3-23416 4-04270 4-85124 5-65978 6-46832 7-27686 1-48379 2-22569 2-96758 3-70948 4-45137 5-19327 5-93516 6-67706 0-87316 1-30975 1-74633 2-18291 2-61949 3-05607 3-49265 3-92924 0-72930 1-09395 1-45860 1-82325 2-18789 2-55254 2-91719 3-28184 1-06043 1-59065 212086 2-65108 3-18130 3-71151 4-24173 4-77194 0-7S673 1-18009 1-57346 1-96683 2-36019 2-75356 3-14692 3-54029 1-16974 1-75460 2-33947 2-92434 3-50921 4-09407 4-67894 5-26381 1-69036 2-53554 3-38072 4-22590 5-07108 5-91626 6-76144 7-60662 1-12734 1-69101 2-25469 2-81836 3-38204 3-94571 4-50938 5-07305 1-40278 2-10417 2-80556 3-50695 4-20834 4-90973 5-61112 6-31251 0-27447 0-41171 0-54894 0-68618 0-82342 0-96066 1-09789 1-23513 0-78049 1-17073 1-56097 1-95122 2-34146 2-73170 3-12194 3-51219 0-68619 1-02929 1-37238 1-71548 2-05857 2-40167 2-74476 3-08786 1-56757 2-35135 3-13514 3-91892 4-70270 5-48649 6-27027 7-05406 1-78378 2-67568 3-56757 4-45946 5-35135 6-24324 713514 8-02703 1-60520 2-40780 3-21040 4-01300 4-81560 5-61820 6-42080 7-22340 . x x 2 676 APPENDIX. TABLE V. SPECIFIC GRAVITY AND ABSOLUTE WEIGHT OF SEVERAL GASES. Specific gravity, atmospheric air = 1-0000. 1 litre (1000 cubic centi- metres) of gas at C. and '76 metre bar. pres- sure weighs grammes. Atmospheric air . " v 1-0000 1-29366 Oxygen . ,] ' , 1-10832 1-43379 Hydrogen ., . . 0-06927 0-08961 Water, vapor of. . i , 0-62343 080651 Carbon, vapor of , ; , . 0-83124 1-07534 Carbonic acid 1-52394 1-97146 Carbonic oxide . . 0-96978 1-25456 Marsh gas . * 0-55416 0-71689 Elayl gas . . ' : : , '''} 0-96978 1-25456 Phosphorus, vapor of , 4-29474 5-55593 Sulphur, vapor of . , 6-64992 8-60273 Hydrosulphuric acid . j .- 1-17759 1-52340 Iodine, vapor of. 8-78898 113-6995 Bromine, vapor of 5-53952 7-16625 Chlorine . . 2-45631 3-17763 Nitrogen . 0-96978 1-25456 Ammonia 0-58879 0-76169 Cyanogen 1-80102 2-32991 APPENDIX. 677 TABLE VI. COMPARISON OP THE DEGREES OF THE MERCURIAL THERMOMETER WITH THOSE OF THE AIR THERMOMETER. According to Dulong and Petit. Degrees of the mercurial Degrees of the air thermometer. thermometer. 105 110 120 130 140 150 160 170 180 190 200 210 104-8 109-6 119-5 129-2 139-0 148-7 158-4 168-0 177-7 187-4 197-0 206-7 Degrees of the mercurial thermometer. 230 240 250 260 270 280 290 300 320 340 350 Degrees of the air thermometer. 216-2 225-9 235-4 245-0 254-6 264-0 273-5 283-2 292-7 311-6 330-5 340-0 According to Magnus. Degrees of the mercurial thermometer. Degrees of the air thermometer. 100 100-00 150 148-74 200 197-49 250 245-39 300 294-51 330 320-92 According to Eegnault. Air thermometer. Mercurial thermometer. 50 50-2 100 100-0 150 150-0 200 200-0 250 250-3 300 301-2 325 326-9 350 ... . 353-3 678 APPENDIX. TABLE FOR THE CONVERSION OF DEGREES INTO DEGREES OF Cent. Fahr. Cent. Fahr. Cent. Fahr. Cent. Fahr. o o 50 58-0 3 26-6 44 111-2 91 195-8 49 56-2 2 28-4 45 113-0 92 197-6 48 54-4, 1 30-2 46 114-8 93 199-4 47 52-6 32-0 47 116-6 94 201-2 46 50-8 + 1 33-8 48 118-4 95 203-0 45 49-0 2 35-6 49 120-2 96 204-8 44 47'2 3 37'4 50 122-0 97 206-6 43 45-4 4 39-2 51 123-8 98 208-4 42 43-6 5 41-0 52 125-6 99 210-2 41 41-8 6 42-8 53 127-4 100 212-0 _40 40-0 7 44-6 54 129-2 101 213-8 39 38-2 8 46-4 55 131-0 102 215-6 38 36-4 9 48-2 56 132-8 103 217-4 37 34-6 10 50-0 57 134-6 104 219-2 36 32-8 11 51-8 58 136-4 105 221-0 35 30-0 12 53-6 59 138-2 106 222-8 34 29-2 13 55-4 60 140-0 107 224-6 33 27-4 14 57-2 61 141-8 108 226-4 32 25-6 15 59-0 62 143-6 109 228-2 31 23-8 16 60-8 63 145-4 110 230-0 30 22-0 17 62-6 64 147-2 111 231-8 29 20-2 18 64-4 65 149-0 ]12 233-6 28 18-4 19 66-2 66 150-8 113 235-4 27 16-6 20 68-0 67 152-6 114 237-2 26 14-8 21 69-8 68 154-4 115 ' 239-0 25 13-0 22 71-6 69 156-2 116 240-8 24 11-2 23 73-4 70 158-0 117 242-6 23 9-4 24 75-2 71 159-8 ]18 244-4 22 7-6 25 77-0 72 161-6 119 246-2 21 - 5-8 26 78-8 73 163-4 320 248-0 _20 4-0 27 80-6 74 165-2 121 249-8 19 2-2 28 82-4 75 ]67'0 122 251-6 18 0-4 29 84-2 76 168-8 123 253-4 17 + 1-4 30 86-0 77 170-6 124 255-2 16 3-2 31 87-8 78 172-4 125 257-0 15 5-0 32 89-6 79 174-2 126 258-8 14 6-8 33 91-4 80 176-0 127 260-6 13 8-6 34 93-2 81 177-8 128 262-4 12 10-4 35 95-0 82 179-6 129 264-2 11 12-2 36 96-8 83 181-4 130 266-0 10 14-0 37 98-6 84 183-2 131 267-8 9 15-8 38 100-4 85 185-0 132 269-6 8 17-6 39 102-2 86 186-8 133 271-4 7 19-4 40 104-0 87 188-6 134 273-2 6 21-2 41 105-8 88 190-4 135 275-0 5 23-0 42 107-6 89 192-2 136 276-8 4 24-8 43 109-4 90 194-0 APPENDIX. 679 OF THE CENTIGRADE THERMOMETER FAHRENHEIT'S SCALE. Cent. Fahr. Cent. Fahr. Cent. Fahr. Cent. Fahr. 137 278-6 183 36l-4 229 444-2 275 527-0 138 280-4 184 363-2 230 446-0 276 528-8 139 282-2 185 365-0 231 447-8 277 530-6 110 284-0 186 366-8 232 449-6 278 532-4 Ul 2S5-8 187 368-6 233 451-4 279 534-2 142 287-6 188 370-4 234 453-2 280 536-0 143 28^-4 189 372-2 235 455-0 281 537-8 144 291-2 190 374-0 236 456-8 282 539-6 145 293-0 191 375-8 237 458-6 283 541-4 146 294-8 192 377-6 238 460-4 284 543-2 147 296-6 193 379-4 239 462-2 285 545-0 148 298-4 194 381-2 240 464-0 286 546-8 149 300-2 195 383-0 241 465-8 287 548-6 150 302-0 196 384-8 242 467-6 288 550-4 151 303-8 197 386-6 243 469-4 289 552-2 152 305-6 198 388-4 244 471-2 290 554-0 153 307-4 199 390-2 245 473-0 291 555-8 154 309-2 200 392-0 246 474-8 292 557-6 155 311-0 201 393-8 247 476-6 293 559-4 156 312-8 202 395-6 248 478-4 294 561-2 157 314-6 203 397-4 249 480-2 ; 295 563'0 158 316-4 204 399-2 250 482-0 i 296 564'8 159 318-2 205 401-0 251 483-8 297 566-6 160 320-0 206 402-8 252 4S5-6 298 568-4 161 321-8 207 404-6 253 487-4 299 570-2 162 323-6 208 406-4 254 489-2 300 572-0 163 325-4 209 408-2 255 491-0 301 573-8 164 327-2 210 410-0 256 492-8 302 575-6 365 329-0 211 411-8 257 494-6 303 577-4 166 330-8 ' 212 413-6 258 496-4 304 579-2 167 332-6 213 415-4 259 498-2 305 581-0 168 334-4 214 417-2 260 500-0 306 582-8 169 336-2 215 419-0 261 501-8 307 584-6 170 338-0 216 420-8 262 503-6 308 586-4 171 339-8 217 422-6 263 505-4 309 588-2 172 341-6 218 424-4 264 507-2 310 590-0 173 343-4 219 426-2 265 509-0 311 591-8 174 345-2 220 428-0 266 510-8 312 593-6 175 347-0 221 429-8 267 512-6 313 595-4 176 348-8 222 431-6 268 514-4 314 597-2 177 350-6 223 433-4 269 516-2 315 599-0 178 352-4 224 435-2 270 518-0 316 600-8 179 354-2 225 437-0 271 519-8 317 602-6 180 356-0 226 438-8 272 521-6 318 604-4 181 357-8 227 440-6 273 523-4 319 606-2 182 359-6 228 442-4 274 525-2 320 608-0 680 APPENDIX. TABLE VIII. WEIGHTS AND MEASURES. GRAMMES. 1 2 3 4 5 CENTIGRAMMES. 1 2 3 4 5 6 7 8 METRES. 1 2 3 4 5 CENTIMETRES. 1 2 3 4 5 6 7 8 9 GRAINS. 35-4346 DECIGRAMMES. 1 = 30-8692 2 46-3038 3 61-7384 4 771730 5 92-6076 6 108-0422 7 123-4768 8 138-9114 9 GRAINS. MILLIGRAMMES. 1543 1 : 3086 2 4630 3 6173 4 7717 5 9260 6 1-0804 7 1-2347 8 1-3891 9 INCHES. DECIMETRES. 39-37 1 78-74 2 118-11 3 157-48 4 196-85 5 236-22 6 275-59 7 314-96 8 354-33 9 INCHES. MILLIMETRES. 3937 1 7874 2 1-1811 3 1-5748 4 1-9685 5 2-3622 6 2-7559 7 3-1496 8 3-5433 9 GRAINS. 1-5434 3-0869 4-6304 6-1738 7-7173 9-2607 10-8042 12-3476 13-8911 GRAINS. 0154 0308 0463 0617 0771 0926 1080 1234 1389 INCHES. 3-937 7-874 11-811 15-748 19-685 23-622 27-559 31-496 35-433 INCHES. 03937 07874 11811 15748 19685 23622 27559 31496 35433 One kilogramme = 15434 grains. One cubic centimetre = 0'0610 cubic inch. One litre = 61-0271 cubic inches. ALPHABETICAL INDEX. PAGE A. Acetic acid (as reagent) ... 82 Acidimetry . . :-.-: : . 512 Air-bath 44 Alcohol (as reagent) . . 81 Alkaline earths, estimation of, by the alkalimetric method 531 separation from each other . . .324 Alkalimetry 521 method of Descroizilles and Gay-Lussac . . 523 method of Fresenius and Will . . . .527 method of Mohr . . 526 Alumina, estimation of . . . 162 hydrate, properties of . 110 properties and composition of .... Ill separation from the alkalies 326 separation from the alkaline earths . . . .327 Ammonia (as reagent) ... 83 estimation of . . . 149 in mineral and other waters 499 acetate of (as reagent) . 85 arsenio-molybdate of, pro- perties and composition 134 carbonate of (as reagent) 86, 88 molybdate of (as reagent) . 88 nitrate of (as reagent) . 88 oxalate of (as reagent) . 85 phosphate of (as reagent) . 83 phospho-molybdate of, pro- perties . . . .137 succiuate of (as reagent) . 85 separation of, from potassa . 316 soda . 316 soda and potassa 316 and magnesia, arsenate of, properties and composi- tion of . . . .133 Aramonio-bichloride of platinum, pro- perties and composition of 103 phosphate of magnesia, pro- perties and composition of 109 Ammonium, chloride of (as reagent) 86, 89 properties and composition 103 sulphide of (as reagent) . 85 Analyses, calculation of . . . 452 general mode of proceeding 48 indirect, calculation of re- sults . . . .459 preparation of substances for . . . .34 of organic compounds con- taining inorganic sub- stances . . . 443 volumetric ... 78 Analytical notes and experiments . 627 Antimonious acid, properties and com- position of . . . .130 Antimony, determination of . . 656 properties of . . .131 teroxide, determination of 221 separation from the bases of groupsl. V. 368 from arsenic and tin . 656 from gold, platinum, and tin .... 376 tersulphide, properties and composition of . . 130 Arsenic (arsenious and arsenic acids), separation from the bases of groups I. "V. . . . 368 from antimony, gold, pla- tinum and tin . . .376 from antimony and tin . . 656 acid, determination of . . 226 separation from arsenious acid 376 tersulphide of, properties and composition of . . 132 Arsenious acid (as reagent) . . 92 determination of . 226 separation from arsenic acid . . . 376 and arsenic acids, se- paration from all other acids . . 381 Ashes of plants, analysis of . . 531 calculation of results of analysis . . 592 682 ALPHABETICAL INDEX. PAGE Atmospheric air, analysis of . . 607 determination of oxy- gen and nitrogen . 611 determination of water and carbonic acid . 607 B. Balance 7 Barium, chloride of (as reagent) . 86 Baryta, acetate of (as reagent) . . 86 carbonate of (as reagent) . 86 properties and com- position of . .105 determination of . . . 153 hydrate of (as reagent) . 83, 88 separation from potassa, soda, and ammonia . . . 320 sulphate, properties and com- position of ... 104 Bismuth, carbonate, properties and composition of . .127 chromate, properties of . 127 teroxide, determination of . 214 properties and compo- sition of . . . 126 separation from the bases of groups I. IV. ... 355 separation from lead . 360 separation from mer- cury . . .360 separation from silver . 360 sulphide, properties and composition of . 127 Bones, analysis of ground . . 605 Boracic acid*, determination of . . 254 separation from the bases 255 separation from phos- phoric acid . . 382 Bromide of silver, properties and composition of . . . . 140 Bromine, estimation of free . . 286 separation from chlorine, 388, 395 from the metals 286 Burette . " . < . . .28 C. Cadmium, oxide and carbonate, pro- perties and composition of . . .128 oxide, determination of . 216 separation from the bases of groups I. IV. . 355 from bismuth . 360 from copper . 3oO from lead . 360 from mercury . 360 from silver . 360 sulphide, properties and composition of .128 Calcium, chloride of (as reagent) 87, 97 borofluoride, properties and composition . . . 138 fluoride (as reagent) . . 87 properties and com- position of . .139 PAGE Calculation of analyses . . . 452 tables . . 658 Cane sugar, conversion into grape sugar . . . 579 Carbonic acid, determination of . 260 determination of, in at- mospheric air . 607 separation from bases . 263 separation from all other acids . . 385 determination in mi- neral waters . 496 Carbon, determination in nitrogenous organic bodies . . . 423 determination in non- nitro- genous organic bodies . 402 Chloric acid, determination of . . 313 separation from other acids . . . .396 the bases . 313 Chloride of ammonium and bichloride of platinum, properties and composition of . 103 ammonium, properties and composition of . . 103 ammonium (as reagent) 86, 89 barium (as reagent) . 86 calcium (as reagent) 87, 97 lead, properties and com- position of . . .122 potassium, properties and composition of . .100 potassium and bichloride of platinum, properties and composition of . 100 silver, properties and com- position . . .119 sodium, properties and composition of .102 sodium and bichloride of platinum, properties and composition of . ^ strontium (as reagent) . Chlorimetry ..... Chlorine (as reagent) . determination of free 102 86 533 82, 89 281 n organic compounds 442 . separation from metals . 279 Chrome iron, analysis of . . . 343 Chromic acid, determination of . 232 separation from other acids pf group I. . 361 separation from bases 234 Chromium, sesquioxicle, determina- tion of . .163 properties and com- position of . Ill hydrated, properties 111 separation from the alkalies . . 326 separation from the alkaline earths 327 separation from alu mina . 330 Clays, analysis of ... 549 Cobalt, properties of . . 116 ALPHABETICAL INDEX. 683 Cobalt, protoxide, determination of 173 separation from the alkalies 331 from the alkaline earths . . 332 from alumina and sesquioxide of chromium . 336 from manganese 336 from nickel . 336 from zinc . 336 protoxide, hydrated, pro- perties of . 116 sulphate, pro- perties and composition 117 protosesquioxide, properties and composition of . . 116 sesquioxide, nitrite of, and potassa, properties and composition of . .117 sulphide, properties and com- position . . . 117 Copper (as reagent) ., V 84,96 properties of . . .124 volumetric determination in copper ores *> "V-l 561 oxide of (as reagent) . . 93 determination of . 206 properties and com- position of . .125 separation from the bases of groups I. IV. . . .355 from bismuth . 360 from lead . 360 from mercury . 360 from silver . 360 pyrites, analysis of . . 561 subsulphide of, properties of 126 sulphide of, properties and composition of . 125 sulpho-subcyanide of, pro- perties and composition of 126 Cyanide of potassium (as reagent) . 86 silver, properties and com- position of . . . 120 Cyanogen, separation from chlorine bromine, and iodine . 395 separation from metals . 297 D. Decantation 64 Decomposition by fluxing . . 56 Desiccation, or drying Dextrine, conversion into grape sugar 577 Directions for weighing . . .15 Division, mechanical ... 35 Dolomites, analysis of ... 552 Drying .... . 37 of precipitates ... 75 Drying disk . . . . ." ff Elutriation . Equivalent of organic bodies, determi- nation of ... . 63 PAGE ther (as reagent) . . . .81 Evaporation . .... 57 Exercises for practice . . . 616 Experiments and notes . . . 627 F. Ferro- and ferricyanides, analysis of . 298 Filtering apparatus .... 65 stands .... 67 Filtration 65 Fluids, measuring of . .24 Fluoride of calcium (as reagent) . 87 properties and com- position of .139 Fluorine, separation from metals . 259 Fluorides, separation from borates . 383 from silicic acid and silicates 383 Fluxing 56 Formulae, empirical, deduction of . 465 rational . . . .468 Funnels 66 G. Galena, analysis of . 561 Gas, as fuel in organic analysis . 448 Gases, measuring of . . . .18 Gold, properties of . . . .128 teroxide, determination of . 217 separation from the bases of groups I. V. . . 367 tersulphide, properties of . 129 Grape sugar, determination of . . 577 Guano, analysis of . . . . 603 Gunpowder, analysis of . . .545 residues, analysis of . 388 H. Heating precipitates to redness . 74 Hydriodic acid, determination of . 287 separation from acids of the first group . 341 Hydrobromic acid, determination of 285 separation from acids of the first group . 386 Hydrochloric acid (as reagent) . . 82 determination of . 275 separation from acids of the first group . 386 Hydrocyanic acid, determination of . 296 separation from acids of the first group . 386 Hydrofluoric acid, determination of . 258 Hydrofluosilicic acid (as reagent) . 82 determination, &c. 241 Hydrogen (as reagent) ... 89 in nitrogenous organic bodies, determination of 423 in non-nitrogenous organic bodies, determination of . 402 Hydrosulphuric acid (as reagent) . 82 determination of 300 separation from acids of the first group . 386 684 ALPHABETICAL INDEX. Hyposulphurous acid, determination, &c. . 237 I. Inorganic bodies, detection of, in or- ganic compounds 401 determination of, in organic compounds 443 lodic acid, determination, &c. . 237 Iodide of silver, properties and com- position of . . . .140 Iodine (as reagent) ... 91 Iodine, determination of free . . 291 separation from chlorine, 391, 394 bromine and chlorine . 393 metals . . 290 Iron, analysis of cast . . . 572 ores . . . 556 protoxide, determination of . 176 separation from ses- quioxide . . 336 ammonio - sulphate (as reagent) . 91 sulphate (as reagent) 87 and sesquioxide, se- paration from al- kalies . . 331 alkaline earths 332 alumina and sesquioxide of chromium . 336 cobalt . . 336 nickel . . 336 zinc . . 336 sesquichloride of (as reagent) . 87 sesquioxide, determination of . 182 properties and com- position of . . 118 acetate, properties and composition of . 119 arsenate, properties and composition of 183 phosphate, properties and composition of 135 succinate, properties and composition of ... 119 sulphide, properties and com- position of . . .118 volumetric determination in ores 559 Lead, acetate (as reagent) . . 88 arsenate, properties and com- position of ... 132 carbonate, properties of . . 121 chloride, properties and com- position of ... 122 chromate, properties of . . 134 (as reagent) . . 94 oxalate, properties of. .121 oxide (as reagent) . . 85 PA OB Lead, oxide, determination of . . 196 properties and composi- tion of ... 121 separation from the bases of croups I. IV. . 355 from mercury . . 360 from silver . , 360 phosphate, properties of .135 sulphate, properties and com- sitionof . . . .121 sulphide, properties and com- position of ... 122 Levigation ..... 36 Lime (as reagent) .... 83 determination of . . . 156 separation from baryta . . 324 potassa, soda, and ammo- nia . . 320 strontia . 324 carbonate, properties and com- position of . . .107 oxalate, properties and com- position of . . .107 sulphate, properties and com- position of. . . .107 superphosphate, analysis of . 606 Limestones, analysis of . . . . 552 Lithia, determination of . . . 152 separation from the other al- kalies . . . .319 Litmus, tincture of (as reagent) . 90 M. Magnesia, determination of . . 159 properties and composi- tion of ... HO separation from baryta and strontia . . . 324 from lime . 324 from potassa, soda, and am- monia . . 320 phosphate, properties . 135 pyrophosphate, properties and composition of . 109 sulphate, properties and composition of . .108 (as reagent) . 87 and ammonia, arsenate of, properties of . . . 133 and ammonia, basic phos- phate of, properties and composition of . . . 109 Manganese, carbonate, properties and composition of . .113 ores, analysis of . . 539 protoxide, determination of . . .168 separation from alkalies . 331 from alkaline earths . 332 from alumina and sesqui- oxide of chro- . mium. . 336 ALPHABETICAL INDEX. 685 PAGE Manganese, separation from zinc . 336 protoxide, hydrated, pro- perties and composition of . ' .114 protosesquioxide, proper- ties and composition of 114 sulphate, properties and composition of . .114 sulphide of, properties of 114 Manures, analysis of ... 602 Marls, analysis of . . . . 552 Measuring . . . . .17 cylinders ... 26 flasks .... 24 Mercury, properties of . . 123 (oxide and suboxide) sepa- ration from the bases of groupsl. IV. . . 355 separation from metals whose chlorides are non-volatile 364 separation from silver . 359 chloride of (as reagent) . 88 oxide (as reagent) . . 85 oxide, properties and com- position of . .124 oxide, determination of . 201 subchloride, properties and composition of . .123 suboxide, determination of . 200 separation of, from oxide of mer- cury . . . 360 phosphate, properties of . 137 sulphide, properties and com- position of . . . 124 Milk sugar, conversion into grape sugar .... 580 Mineral waters, analysis of . . 482 determination of spe- cific gravity of . 492 Molybdic acid, determination of . 231 Mortars 36 N. Nickel, protoxide, determination of . 171 properties and com- position of . 115 separation from the alkalies . 331 from the alkaline earths . 332 alumina and ses- quioxide of chro- mium . 336 manga- nese and zinc . 336 hydrated, proper- ties of . . 115 sulphide, properties of . . 115 Nitric acid (as reagent) ... 81 determination of . .307 Nitric acid, separation from bases . from other acids Nitrogen of the air, determination of Nitrogen, detection of, in organic substances . . . determination of, in or- ganic compounds . properties of . . . Nitrohydrochloric acid (as reagent) . PAGE 307 396 611 400 423 104 82 O. Oil-bath Organic analysis Organic substances, examination of, for inorganic constituents . for nitrogen and . sulphur for phosphorus . qualitative exa- mination of . Oxalic acid (as reagent) . determination of . separation from bases separation from phos- phoric acid from other acids of first 43,47 group Oxygen (as reagent) 401 400 401 90 257 258 381 95 P. Palladium, protiodide, properties and composition of . . 141 protoxide, determination of .... 216 sodio-protochloride of (as reagent) ... 88 Phosphoric acid, determination of . 242 separation from the acids of group I. . 382 separation from the bases . . .248 Phosphorus, detection of, in organic bodies . . .401 determination of, in or- ganic bodies . . 442 Platinum, properties of . . . 129 bichloride (as reagent) . 88 binoxide, determination of 218 separation from the bases of groups I. V. . . 367 from gold . . 375 bisulphide, properties of . 129 potassio-bichloride, proper- ties and composition of . 100 Pipette 27 Plants, analysis of ashes of . . 581 calculation of results . . 592 Potassa (as reagent) . . .83, 96 determination of . .144 bichromate of (as reagent) .86, 97 bisulphate of (as reagent) . 88 chlorate of (as reagent) . 94 nitrate of (as reagent) . 88 686 ALPHABETICAL INDEX. Potassa, nitrate of, properties and composition of . nitrite of (as reagent) . permanganate of (as reagent) solution of (as reagent) sulphate, properties and composition of Potassio-bichl< ride of platinum, pro- perties and composition of . Potassium, chloride of, properties and composition Potassium, 03 anide of (as reagent) . iodide of (as reagent) . Pounding Precipitation Eeagents Salt, common, analysis of Selenious acid, determination, &c. Silicates, fluorides, and phosphates, separation from each other Silicic acid, determination of . properties and composi- tion of ... separation from other acids from bases from fluorine . Silicates, mixed, analysis of Silicofluoride of barium, properties and composition of Silver (as reagent) .... Silver in lead ores, determination of . Silver, properties of ... bromide, properties and com- position of ... chloride, properties and com- position of ... cyanide, properties and comp. iodide, properties and compo- sition of .... oxide, determination of separation from the bases of groups I. IV. nitrate of (as reagent) . phosphate, properties and com- > position of . pyrophosphate of . sulphide, properties of . Soda (as reagent) .... determination of separation from potassa . acetate of (as reagent) biborate of (as reagent) . bicarbonate of (as reagent) bisulphite of (as reagent) . carbonate of (as reagent) . and potassa, carbonate of (as reagent) .... carbonate, properties and coni- . position of . lime (as reagent) 99 100 100 86 92 35 63 544 236 384 139 385 547 105 562 119 140 119 120 140 188 355 137 137 120 83 147 316 85 88 96 86 10-2 PAGE Soda, nitrate of, properties and com- position of . . . .101 sulphate of, properties and com- position of . . . .101 Sodio-Hchloride of platinum, pro- perties and composition . .102 Sodium, chloride of (as reagent) . 92 properties and composition of . . 102 Soils, analysis of. . . . . 594 Solution of substances ... 55 Starch, conversion into grape sugar . 579 Strontia, determination of . . 154 separation from baryta . 324 from potassa, soda, and ammonia . 320 carbonate, properties and composition of . .106 sulphate of ... 106 Strontium, chloride of (as reagent) . 86 Sugars, quantitative estimation of . 576 Sulphide of ammonium (as reagent) . 85 bismuth, properties and composition of . .127 cadmium, properties and composition of . .128 cobalt, properties and com- position of . . .117 copper, properties and com- position of . . .125 gold, properties and com- position of . . . 129 iron, properties and com- position of . . .118 lead, properties and com- position of . . .122 manganese, properties . 114 mercury, properties . 124 nickel, properties . 115 platinum, properties . 129 silver, propertiesand com- position of . . . 120 sodium (as reagent) . 85 zinc, properties and com- position of . .113 Sulphur, detection of, in organic sub- stances . . . .400 determination of, in organic substances . . . 438 separation and determination in metallic sulphides . 303 Sulphuretted hydrogen, determination of .... 300 (as reagent) . 82 separation from acids of the first group 386 Sulphuric acid (as reagent) . . 82 determination of . 238 separation from other acids . . .381 separation from bases . 2iO Sulphurous acid (as reagent) . . 92 determination, &c. . 237 ALPHABETICAL INDEX. 687 Tartaric acid (as reagent) . . 82 Tin (protoxide and binoxide) determi- nation of . . . . 225 separation from the bases of groups I. V. . . . 367 from gold and pla- tinum . . 375 Tin, binoxide, properties and compo- sition of . . . .131 binoxide, phosphate, properties . 137 protochloride of (as reagent) . 88 sulphide, properties and compo- sition of . . . .132 Titanic acid, determination of . .165 U. Ultimate analysis of organic bodies . 398 analysis of organic bodies containing chlorine (bro- mine or iodine) . . 442 analysis of organic bodies containing sulphur . . 438 analysis of organic bodies free from nitrogen which are volatile, or change at 212 F 419 analysis of organic non- vola- tile readily combustible solid bodies free from nitrogen . . . 403 analysis of organic non-vola- t tile difficultlycombustible solid bodies free from nitrogen . . .414 analysis of organic non-vola- tile liquids free from ni- trogen . . . .422 analysis of organic nitroge- nous bodies . . . 423 analysis of organic sub- stances containing inor- ganic bodies . . . 443 analysis of organic volatile fluids free from nitrogen . 419 Uranium, acetate of sesquioxide of (as reagent .... 87 Uranium, phosphate of sesquioxide, properties . . .136 sesquioxide, determination of . . . .187 separation from the oxides of groups I. IV. . 354 V. Vapor, determination of the density of 472 Volume, determination of (measuring) 17 Volumetric analysis . . .78 W. Washing bottles .... 69 Washing precipitates ... 68 Waters, analysis of . . . . 479 Water (as reagent) .... 81 in atmosphere, determination of 607 estimation of . . .50 -bath, for drying . . .41 Weighing 13, 49 residues left by evaporation 62 Weights . . . . . . 12 Z. 83 Zinc (as reagent) .... carbonate, properties and com- position of . . . .112 oxide, determination of . . 166 properties and com posi- tion of . . . separation from alkalies . from alkaline earths . from alumina and sesqui- oxide of chromium . sulphide of, properties and com- position of . . . . Zinc ores, analysis of ... volumetric determination of . . 112 331 332 336 113 567 568 Page 7, 1 Iff, ERRATA. ne 1 from top, for Division, read Part. 3 > fw Section, read Division. 6 ,, for Chapter, read Section. , 3 from bottom, for Ammonia, read Soda. , 22 ,, for Sulphuric, read Sulphurous. THE END. 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