UNIVERSITY OF CALIFORNIA 
 AT LOS ANGELES
 
 A COLLEGE TEXT-BOOK 
 
 ON 
 
 QUANTITATIVE ANALYSIS
 
 THE MACMILLAN COMPANY 
 
 NKW YORK BOSTON CHICAGO - DALLAS 
 ATLANTA SAN FRANCISCO 
 
 MACMILLAN & CO., LIMITED 
 
 LONDON BOMBAY CALCUTTA 
 MELBOURNE 
 
 THE MACMILLAN CO. OF CANADA, LTD. 
 
 TORONTO
 
 A COLLEGE TEXT-BOOK 
 
 ON 
 
 QUANTITATIVE ANALYSIS 
 
 BY 
 
 HERBERT RAYMOND MOODY, S.B. (M.I.T.), A.M., 
 PH.D. (COLUMBIA) 
 
 ASSOCIATE PROFESSOR OF ANALYTICAL AND APPLIED CHEMISTRY 
 COLLEGE OF THE CITY OF NEW YORK 
 
 THE MACMILLAN COMPANY 
 
 1919
 
 COPYRIGHT, 1912, 
 BY THE MACMILLAN COMPANY. 
 
 Set up and electrotyped. Published September, 1912. Reprinted 
 June, 1914; May, 1916; February, 1917. 
 
 NortoooS Khfss: 
 Berwick & Smith Co., Norwood, Mass., U.S.A.
 
 I'M 
 
 IATI 
 
 ACKNOWLEDGEMENT 
 is MADE 
 
 TO MY WIFE 
 
 EDNA WADSWORTH MOODY (M. I. T., 1893) 
 
 WITH WHOSE EFFICIENT COLLABORATION 
 THIS BOOK HAS BEEN WRITTEN. 
 
 I AM INDEBTED TO 
 
 PROFESSOR LEO FRANK GUTTMANN, PH.D., F.I.C., F.C.S., 
 
 OF QUEEN'S UNIVERSITY, KINGSTON, ONTARIO, 
 
 FROM WHOM I RECEIVED HELPFUL SUGGESTIONS 
 
 WHEN ORIGINALLY LAYING DOWN THIS COURSE, 
 
 FOR CRITICISMS AND PROOF READING.
 
 \N THIS book is issued with no thought of enriching the literature 
 
 *$\of Quantitative Analysis. The field has been covered so often 
 \ and the number of typical analyses suitable for elementary 
 
 Q\ classes is so limited that no great departure from regulation courses 
 
 j. is possible. 
 
 The aim in view has been to prepare directions which shall be 
 
 **s explicit, clear, adapted to those to whom quantitative analysis 
 . with its refinements is an unknown field and above all to make 
 
 obvious the unnecessary pitfalls that consume time. For the last 
 
 r reason the author has placed the explanatory facts in large type 
 on the same page and directly under the directions for procedure to 
 which they relate. While this book has been in use in manuscript 
 form during the last five years at the College of the City of New 
 York this has been effective in two hoped for results: (1) The pre- 
 vention of mistakes that are so often made before the student has 
 turned to the end to read the explanations and warnings in the 
 notes and (2) a clearer understanding of the reactions and changes 
 at each step of the work. 
 
 Another object in view has been to make a book that will be 
 useful to the student who is either taking up quantitative work by 
 himself or with an instructor whose classes are too large to admit 
 of much individual attention. This is more often the case than 
 not. It is the writer's experience that for lack of specific directions 
 the student, while the instructor is otherwise engaged, makes the 
 fatal error which necessitates the repetition of perhaps hours of
 
 Vi FOREWORD 
 
 work. There are accepted methods of manipulation, the result 
 of tried experience, that insure correct analyses. The student 
 cannot be expected to know these intuitively. Too much inde- 
 pendence of action at this stage inevitably leads to a loss of time 
 and to the acquiring of disadvantageous habits of manipulation. 
 By the use of these minute directions he at once gets into the habit 
 of correct manipulation, accomplishes more in the same time and, 
 for a beginner, gets unusually good results. 
 
 There is much possible latitude in the choice of detail of methods 
 in the analyses selected, but standard methods which have been 
 found to serve satisfactorily with our own students are those used. 
 
 Only such facts and theories as are necessary to the full under- 
 standing of the development of the subject are included. For 
 further details the student is referred to his instructor's lectures 
 and to larger textbooks. 
 
 The author will gladly confer with instructors in other colleges 
 concerning his system of "unknowns." The substances used for 
 analyses are strictly unknown to the student who is consequently 
 forced to rely upon his own work. A qualitative analysis gives no 
 hint as to which sample has been given to him. 
 
 HERBERT RAYMOND MOODY. 
 
 COLLEGE OF THE CITY OP NEW YORK.
 
 A COLLEGE TEXT-BOOK 
 
 ON 
 
 QUANTITATIVE ANALYSIS
 
 QUANTITATIVE ANALYSIS 
 
 QUANTITATIVE ANALYSIS determines the amount of one or more 
 of the constituents of a substance. The methods used in Quantita- 
 tive Analysis may be considered as refinements of those already 
 used in Qualitative Analysis.* When it is merely a question of 
 determining what elements are present in the substance to be 
 analyzed, these less precise processes of Qualitative Analysis are 
 adequate; when it is a question, however, as in Quantitative 
 Analysis, of determining how much of one or more elements is 
 present, the reactions selected for the process must produce more 
 complete separation. To isolate completely one substance from 
 one or more elements, requires definite, standard conditions ful- 
 filled with the most scrupulous care, neatness and accuracy. To 
 illustrate: 
 
 If ammonium oxalate be added to a mixture of magnesium and 
 calcium chlorids to determine the per cent, of calcium present, 
 difficulties are met by adding too much oxalate, and on the other 
 hand by adding too little. In Qualitative Analysis, an indefinite 
 amount of the ammonium oxalate added to the mixture of mag- 
 nesium and calcium chlorids will precipitate most of the calcium as 
 calcium oxalate and leave most of the magnesium in the filtrate. 
 The presence of calcium is shown, which is all that is required. 
 In Quantitative Analysis, there are two facts that must be taken 
 into consideration. First, if only enough oxalate is added to throw 
 
 * References are given in the text to the preliminary experiments in "Chem- 
 istry of the Metals" which apply in this later course. 
 
 1
 
 2 QUANTITATIVE ANALYSIS 
 
 out the calcium as calcium oxalate, some of the calcium oxalate 
 will dissolve in the magnesium chlorid and make the per cent, of 
 calcium too low. Second, if enough ammonium oxalate is added 
 to convert both the calcium and magnesium to oxalates, then the 
 calcium oxalate will drag down with it some of the magnesium 
 oxalate and make the per cent, of calcium too high. Hence the 
 analyst is between two dangers: (a) he may lose some of the cal- 
 cium because of the solubility _of the oxalate in magnesium chlorid 
 or (b) he may add to the precipitate through contamination. 
 
 Later, when analyzing for calcium and magnesium, the student 
 will be given precautions which reduce these dangers to a mini- 
 mum. Absolute adherence to directions as to quantities, time and 
 manipulation is necessary if the student is to get accurate results. 
 
 A Quantitative Analysis may be made by Gravimetric or Volu- 
 metric methods: 
 
 In Gravimetric Analysis, which includes electrolytic work, meas- 
 urement by weight is the important factor; in Volumetric Analy- 
 sis, measurement by volumes. Electrolytic Analysis involves the 
 isolation of an element by use of the electric current.
 
 SECTION I 
 
 GRAVIMETRIC ANALYSIS
 
 GRAVIMETRIC ANALYSIS 
 
 Apparatus 
 
 THE student is already familiar with most of the apparatus used 
 in gravimetric analysis, such as beakers, evaporating dishes, flasks, 
 lamps, stirring rods, filter papers and funnels. 
 
 The following details should, however, be noted: 
 
 (1) Stirring rods must be rounded with even more care than 
 in qualitative work to avoid the possibilities of spoiling beakers by 
 scratching. Precipitates adhere to such scratches and are removed 
 from them with difficulty. For the complete removal of precipi- 
 tates, stirring rods should have at one end about one inch of black 
 rubber tubing, fitted closely to the rod and just covering the end. 
 This rubber end should not be kept standing in a solution, espe- 
 cially while the solution is boiling. It should be reserved for the 
 latter part of the filtration when the last of the precipitate is 
 being removed from the beaker. Such a stirring rod is known as 
 a "policeman." 
 
 (2) Ordinary filter paper, the sort used in Qualitative Analysis, 
 is not suitable for the final filtration of quantitative precipitates. 
 Such paper is used only in preliminary filtrations, to cover the 
 funnel when it is placed in the drying oven and to place on the 
 filter-stand under beakers during the period of filtration. For the 
 
 5
 
 6 QUANTITATIVE ANALYSIS 
 
 final filtration a special "washed" filter-paper is used. Any of 
 the various grades are suitable. The Schleicher and Schull, 
 No. 589, 11 cm. in diameter, is a convenient size and a satisfactory 
 quality. Each paper has a uniform ash of 0.00017 grams. Allow- 
 ance in the final weighing may therefore be made and this weight 
 of ash deducted from the total weight of the substance in the 
 crucible. Such papers are expensive and should be used only for 
 final filtrations. It is advisable to keep filter papers in envelopes 
 or boxes to prevent them from collecting dust or other ponderable 
 matter. 
 
 (3) Funnels for this work should be of the so-called Bohemian- 
 glass type, with sides at an exact angle of 60 and with a long 
 stem which is ground to a point. A funnel of this shape filters 
 much more quickly than one of the ordinary kind (see fact 7, 
 page 36). 
 
 In addition to the above apparatus, use will be made of: (4) 
 weighing tubes; (5) wash bottles; (6) casseroles; (7) filter flasks; 
 (8) steam baths; (9) air baths; (10) crucibles; (11) triangles; 
 (12) desiccators and (13) the analytical balance. 
 
 (4) Weighing tubes may be of the ground-glass-stopper type 
 with either a flat or round bottom or a 2f-inch by |-inch test tube 
 fitted with a good grade of cork stopper. The latter is equally 
 desirable. 
 
 (5) Wash bottles used in Quantitative Analysis should have tips 
 small enough to emit a sufficiently fine stream of water to avoid 
 spattering precipitates when the stream strikes them. For the 
 convenient handling of a wash bottle containing hot water, the 
 neck should either be wound with cord, covered with cork sheets 
 or supplied with some other similar device. 
 
 (6) Casseroles are more often used than evaporating dishes, 
 altho they serve the same purpose. It is, of course, fatal to an
 
 GRAVIMETRIC ANALYSIS 7 
 
 analysis to lose even a minute amount of the solution. The handle 
 on the casserole makes it much easier to avoid spilling and is more 
 convenient to hold while filtering. 
 
 (7) Filter flasks, or suction bottles, facilitate the filtering of 
 gelatinous and other precipitates. The funnel stem is inserted in 
 a one-hole rubber stopper fitted to the neck and the side-neck is 
 attached to the vacuum outlet by rubber "pressure" tubing. The 
 tip of the stem of the funnel should come well below the side neck. 
 In order to avoid the possibility of the introduction of liquids or 
 corrosive vapors into the vacuum pipes and apparatus, a gas 
 wash bottle must be interposed between the filter bottle and the 
 vacuum cock on the desk. To avoid breaking the tip of the wet 
 filter paper by the increased pressure on it, the apex of the funnel 
 should contain either a perforated platinum cone or a small cone 
 made by folding a "hardened" filter paper, "S. & S." No. 575, 
 7 cm. in diameter. 
 
 (8) Steam Baths are used for evaporations which are rarely made 
 over the free flame because of the possibility of loss through too 
 violent ebullition. If the Bunsen lamp is used, the beaker or 
 casserole should stand either on a sand bath (a shallow iron tray 
 containing a quarter of an inch of sand) or on an iron plate covered 
 with a sheet of asbestos board. 
 
 (9) Air Baths are used for drying precipitates in funnels and for 
 determining water of crystallization, hygroscopic moisture, etc. 
 They may be simple copper ovens with shelves, heated by a lamp, 
 or they may be larger and heated either with a steam jacket or 
 steam pipes in the base. 
 
 (10) Crucibles for all ordinary ignition of precipitates may be of 
 Berlin porcelain in spite of the fact that some precipitates are not 
 so easily brought to a constant weight in porcelain as in platinum 
 crucibles. Such porcelain crucibles should be heated with great
 
 8 QUANTITATIVE ANALYSIS 
 
 care to avoid breaking. However, unless expense prohibits their 
 use, platinum crucibles are far more desirable except in the case 
 of precipitates which are easily reduced; as, for example, those 
 obtained in lead and phosphorus determinations. In such cases 
 the reduced metal will alloy with the platinum and spoil the cru- 
 cible. For work of this kind porcelain crucibles always should 
 be used. 
 
 Two important facts should at this point be learned: 
 
 (1) Platinum alloys with certain metals. A student sometimes 
 forgets this until he has ruined his expensive platinum crucible. 
 
 (2) Before selecting the sort of crucible for use, the chemical 
 change that is to take place in the precipitate which is being ignited 
 should be considered. 
 
 Platinum containers should be used for most fusions and always 
 for the treatment of substances with hydrofluoric acid. 
 
 Whichever crucible is employed, it must first be ignited and 
 cooled in the desiccator before weighing. Otherwise, when it is 
 ignited with the precipitate, the crucible itself might change in 
 weight. 
 
 Crucible covers are always weighed with the crucible, as ignited 
 precipitates should be weighed covered in order to avoid absorp- 
 tion of hygroscopic moisture. Covers, by keeping out the air 
 currents, also prevent the loss of finely divided precipitates during 
 ignition. 
 
 Crucibles must be cleaned after each analysis. Porcelain cru- 
 cibles may be cleaned by using any solvent of the adhering sub- 
 stance which does not react with porcelain. 
 
 If platinum crucibles are used, the student should observe the 
 following rules and precautions issued by J. Bishop & Co., Malvern, 
 Pennsylvania. 
 
 CARE AND USE OF PLATINUM WARE* 
 
 To insure long and satisfactory service, platinum ware should 
 be perfectly clean and bright before each operation in which it is 
 employed, and to that end it is advisable to carefully clean, dry 
 and polish it immediately after it is used. 
 
 * Courtesy of J. Bishop & Co. Platinum Works, Malvern, Pa.
 
 GRAVIMETRIC ANALYSIS 9 
 
 The cleaning may be accomplished by boiling in dilute hydro- 
 chloric acid or by immersing in fused potassium bisulphate 
 for a few minutes and removing the salt by means of boiling 
 water. 
 
 By rubbing the surfaces with moist talc or fine sea sand (free 
 from sharp or angular grains) the platinum may be freed from 
 adhering substances and polished without injury or appreciable 
 loss of metal. 
 
 After polishing, the platinum should be thoroughly rinsed in 
 distilled water and finally ignited. 
 
 PRECAUTIONS TO BE OBSERVED 
 
 In making ignitions or fusions in platinum vessels by means of 
 the Bunsen burner, the upper non-luminous cone only should be 
 employed, and not the inner cone, nor should a smoky flame be 
 used, as the action of a flame containing free carbon will result 
 in the formation of a carbide of platinum, causing the metal to 
 become brittle. 
 
 Fusions in which hydrates of sodium, potassium, barium or 
 lithium are used should not be performed in platinum vessels, 
 as they attack the platinum at high temperatures. Great care 
 should be observed in igniting phosphates in platinum crucibles, 
 as the presence of reducing substances, such as the charcoal of the 
 burnt filters, may cause the reduction of small quantities of phos- 
 phorus, which, combining with the platinum, render it quite 
 brittle. 
 
 Compounds of silver, lead, tin, bismuth, arsenic and antimony 
 should not be ignited in platinum vessels as the reduction of metals 
 having low melting points may result in the formation of alloys 
 with the platinum. 
 
 Evaporations and fusions in which chlorin, iodin or bromin 
 are set free should not be performed in vessels of platinum. 
 
 (11) Triangles. During the process of heating, crucibles are 
 placed upon triangles of such a diameter as to admit of the crucible 
 resting vertically or on its side at an angle of forty-five degrees.
 
 10 QUANTITATIVE ANALYSIS 
 
 For all ordinary purposes "pipe-stem" triangles answer, but those 
 made of heavy platinum wire (gage 18, or heavier) are in some 
 respects better. These latter need not be made entirely of plati- 
 num, but a triangle of platinum wire may be stretched from copper 
 loops at the center of the sides of a larger copper wire triangle 
 (gage 12, or over). The triangle must be kept scrupulously clean. 
 If it has not been well cleaned, after a carelessly regulated fusion, 
 for instance, adhering matter may attach itself to the next cruci- 
 ble heated upon it and increase its weight. 
 
 (12) Desiccators, as the name indicates, furnish an inclosed 
 space in which the air is perfectly dry and from which, therefore, 
 no moisture can be deposited on crucibles or precipitates to add to 
 their weight as they cool. There are various types of desiccators, 
 a most convenient form of which will be found in the five-inch 
 Scheibler which is fitted with a three-hole porcelain crucible plate 
 and filled in the lower chamber with a few sticks of solid potassium 
 hydroxid.* The ground-glass undersurface of the run of the 
 cover should be lightly covered with vaseline or with a mixture of 
 equal parts of beeswax and paraffin melted together. 
 
 (13) The Analytical Balance is sufficiently sensitive to weigh to 
 one ten-thousandth part of one gram. The pillar, beam and the 
 pans are its three most essential parts. The pillar is surmounted 
 by the beam, the halves of which are termed the "arms," two 
 equal divisions of a lever. The beam is supported on a fulcrum 
 at the top of the pillar. The arms are capable of adjustment in 
 length by means of a micrometer screw at the ends. Two equal 
 loads on the two pans, therefore, ^produce equilibrium or equal 
 oscillations on either side of the center. The right-hand arm is 
 divided into five or ten equal parts, each in turn subdivided into 
 ten equal parts. A two-legged piece of platinum wire, called a 
 "rider," may be set down upon this arm at any point by means of 
 the rider hook, which is moved by the rider rod projecting outside 
 of the case at the top of the right-hand side. When placed upon a 
 whole division, the rider is equivalent to a corresponding number 
 
 * Fused anhydrous calcium chlorid can be used if preferred.
 
 GRAVIMETRIC ANALYSIS 11 
 
 of milligrams. The fractions of divisions, consequently, read tenths 
 of milligrams. For accurate results the balance should be level 
 on the table. It may be made so by adjusting the height of the 
 two front legs of the case until the spirit level or plumb bob at 
 the base of the pillar indicates proper adjustment.* Friction in 
 the balance at the point of support must as far as possible be 
 avoided. This is accomplished by using "knife-edges" to give 
 as little supporting surface as possible and by making all support- 
 ing surfaces of hard metal. The "knife-edges" are of hard steel 
 resting upon agate, f 
 
 THE WEIGHTS 
 
 It is rarely necessary in gravimetric work to weigh anything 
 heavier than one hundred grams. A box of weights, therefore, 
 usually contains weights of the following denominations: 
 
 50 grams 
 
 20 grams 
 
 10 grams 
 
 10 grams 
 
 5 
 
 2 
 
 1 gram 
 
 1 gram 
 
 . 5 gram 
 
 0.2 gram 
 
 0.1 " 
 
 0.1 
 
 it 
 
 0.05 " 
 
 0.02 " 
 
 0.01 " 
 
 0.01 
 
 n 
 
 a total of 99.99 grams. 
 
 It is evident that if the weights oxidize or corrode, their value 
 would change. They must therefore be protected from dirt and 
 fumes and must be handled only with forceps. They should never 
 be left out of the box, which should always be kept tightly covered. 
 Pure platinum or gold would be the most permanent materials for 
 weights but for ordinary work their value prohibits their use. 
 The large weights are of brass, tin, etc., and may be platinum or 
 gold plated. Fractional weights are usually of pure platinum. 
 
 * Such adjustments should be made by. the instructor and not by the beginner, 
 whose inexperience is likely to result in making a bad matter worse. 
 
 t For details of construction and theory of the balance, the student is referred 
 to Clowes and Coleman's "Quantitative Analysis," pages 1-14; Morse's "Quan- 
 titative Chemistry," pages 1-30; Fresenius's "Quantitative Analysis," pages 
 1-26; Olsen's "Quantitative Analysis," pages 7-20; and Treadwell's "Analytical 
 Chemistry," Vol. II, pages 6-16.
 
 12 QUANTITATIVE ANALYSIS 
 
 GRAVIMETRIC ANALYSIS is the process of determining the 
 relative amount of a constituent of a substance by: 
 
 (I) Weighing a definite quantity of the substance to be 
 analyzed, 
 
 (II) Isolating the element or radical sought either as the ele- 
 ment itself or as a definite, insoluble, pure compound, 
 
 (HI) Freeing this element or compound from admixed liquids 
 or solids by filtering and washing, 
 
 (IV) Igniting to a stable compound of known composition, 
 
 (V) Weighing the element or stable compound, and 
 
 (VI) Calculating the per cent, from data obtained.
 
 GRAVIMETRIC ANALYSIS 13 
 
 PROCESSES EMPLOYED IN GRAVIMETRIC ANALYSIS 
 
 I. Weighing 
 
 The weight of a substance taken for analysis varies. An or- 
 dinary charge runs from 0.2 gram to 1 gram, but, under some con- 
 ditions, 5 or even 10 grams might be required. Within certain 
 limits the larger the amount taken for analysis the more accurate 
 the result, but no amount should be large enough to give an over 
 bulky precipitate. An analyst in his selection is guided by the 
 quantity of the unknown compound at hand and also by the re- 
 lative amount of the element sought in the substance. If it con- 
 tains a large amount of the element sought, a smaller weight of 
 the substance is taken than if it contains, for example, only a 
 fraction of a per cent. 
 
 A. Precautions 
 
 (1) Always use the same balance. 
 
 (2) Sit directly in front of the balance to avoid parallax. 
 
 (3) Borrow neither weights nor riders from another balance. 
 
 (4) Allow the knife-edges to rest upon the agate bearings only when 
 
 the pans are swinging. At all other times the cradle should' 
 be raised by the knob or wheel in front. Form the habit 
 of immediately raising the cradle the moment equilibrium 
 has been established. 
 
 (5) Never remove weights from the pan nor put them upon it 
 
 unless the beam has been arrested by raising the cradle. 
 
 (6) Never weigh a substance upon the balance pan, but have it in 
 
 a crucible, weighing tube or on a tared watch glass. 
 
 (7) Never put a hot nor a wet dish on the balance pan for it may 
 
 both hurt the surface of the pan and change the weight. A 
 hot dish produces ascending air currents and therefore 
 weighs too little. A dish below the temperature of the 
 balance produces descending currents and therefore weighs 
 too much.
 
 14 QUANTITATIVE ANALYSIS 
 
 (8) Keep the front door of the balance closed except during the 
 
 time of putting on or taking off the weights or dishes. If 
 the balance is provided with side doors, the front door need 
 scarcely ever be opened. The final operation of the weigh- 
 ing with the "rider" should be done with the case entirely 
 closed. If any door is open, air currents may cause an 
 error. 
 
 (9) Weigh all precipitates which are markedly hygroscopic, vol- 
 
 atile or absorbers of carbon dioxid with the crucible cover 
 on. The crucible and cover should therefore be weighed 
 together at the beginning of the analysis. 
 
 (10) Never handle the weights except with the forceps provided 
 
 in the box. 
 
 (11) The center of the pointer scale should be the zero point. 
 
 Unless the balance is in perfect adjustment, this will not 
 be the case. 
 
 Occasionally determine the zero point as follows: 
 Imagine the divisions on the pointer scale numbered from to 
 20 from left to right. Make three readings on the left and two 
 on the right, as, for example: 
 
 2 U 50 l*' g OO 16-63 + 3.08 = 98 
 
 3.00 16.25 
 
 3 75 2)33 25 ^ na ^ * s ' ^ ne zero P m t> 
 
 Q\Q O g Tv/r 9.8, is 0.2 of a space 
 
 3)9,25 Mean, 16.63 at the left of the mid- 
 Mean, 3.08 die division. 
 
 The position of the zero point changes because of varying temper- 
 ature, defective condition of the knife-edges or from jarring. 
 
 B. Method of Weighing . 
 
 Unless special directions are given for weighing in a tared watch 
 glass or crucible, the method of "direct weighing" of the charge 
 is not to be used. The method of "indirect weighing," weighing 
 by difference, is as follows: 
 
 The weighing tube is partially filled with the prepared substance 
 stoppered, carefully wiped, weighed and the weight recorded. 
 The approximate amount of salt is emptied from the tube into a 
 beaker, the stopper replaced and a second weighing made. The
 
 GRAVIMETRIC ANALYSIS 15 
 
 difference between the two weights is the weight of the charge. 
 This process is given in detail under the "Determination of 
 Aluminium." 
 
 The weight of the charge specified in the directions is only ap- 
 proximate. For example, if the directions call for 0.5 gram, a 
 charge weighing 0.4895 gram or one weighing 0.5103 gram fulfills 
 the conditions. 
 
 C. Directions for Weighing 
 
 (1) With tongs, take the article to be weighed and put it through 
 
 the side door on the center of the left-hand pan. 
 
 (2) If the article has never been weighed before,* trials should 
 
 be made, according to (3), to determine which one or com- 
 bination of two or more of the larger weights comes the 
 nearest to causing equilibrium. During such trials, the 
 cradle should be lowered but part way and the pointer carefully 
 watched in order to avoid the violent descent of either pan, 
 which may put the balance out of adjustment. 
 
 (3) With the forceps, put the large weight selected on the center 
 
 of the right-hand pan. If the right-hand pan descends, the 
 weight is too large and the next smaller denomination should 
 be used. If this proves too light, add smaller weights till 
 the total weight just falls short of balancing the article on the 
 left pan and finish with the rider. For example: A twenty 
 gram weight proves too heavy. Raise the cradle. Remove 
 the twenty-gram weight. Put on a ten-gram weight. Partly 
 lower the cradle carefully. This is too small. Raise the 
 cradle. Try a combination of ten and five. Lower the 
 cradle. This is not enough. Raise the cradle. Make a 
 combination of ten, five and two. Lower the cradle. This 
 is not enough. Raise the cradle. Add one gram. Lower 
 the cradle. This causes the right-hand pan to descend. 
 Raise the cradle and put the one-gram weight back into its 
 place in the box. Proceed with the smaller fractional 
 weights until the last one added just falls short of causing 
 equilibrium. Close the door and determine the exact 
 position of the rider necessary to produce equilibrium. 
 
 * Forjthe student's guidance, it may be stated that an average porcelain cru- 
 cible and cover weighs about 16 grams, an average 15 c.c. platinum crucible and 
 cover about 12 grams and a 2J inch-platinum evaporating dish about 30 grams.
 
 16 QUANTITATIVE ANALYSIS 
 
 Experience teaches by observing the swing of the pointer, about 
 how much too heavy or how much too light a given mass is 
 and will help to determine the next combination. 
 
 After equilibrium has been established: 
 
 (4) Raise the cradle. 
 
 (5) Add up the weights on the pan and record in the notebook. 
 
 This should be done in ink and at once. This rule is 
 insisted upon.* 
 
 (6) Check this result by noting the empty spaces in the box. 
 
 (7) Remove the weights with the forceps and put each in its 
 
 proper place in the box. 
 
 (8) Remove the crucible or other container. 
 
 (9) Close the doors. 
 
 (10) Lift the rider. 
 
 (11) Call the Instructor's attention at once to anything that may 
 
 have been spilled within the balance or to any part of the 
 balance that may have become disarranged. 
 
 * For the first two analyses, all recorded weights should be stamped "checked " 
 by the Instructor before the weights are removed from the pan. This not only 
 insures good work on the student's part but corrects errors due to inexperience.
 
 GRAVIMETRIC ANALYSIS 17 
 
 n. Isolating the Element or Radical Sought 
 
 SOLUTION OF THE SUBSTANCE 
 
 Getting the original substance into solution is the first necessary 
 step in the process leading up to precipitation. A water solution 
 is usually preferable. If it cannot be dissolved in water it should 
 be dissolved in acid. Here a knowledge of solubilities is essential. 
 For instance, an alloy or compound containing lead should be 
 dissolved in an acid like nitric acid. An unthinking analyst 
 might try sulfuric acid, not recalling the fact that lead sulfate 
 is insoluble and that therefore no solution could result. Many 
 compounds and ores are wholly or in part insoluble in acids, cold 
 or hot, or even in aqua regia. Such substances should first be 
 made to undergo a preliminary fusion to change them to soluble 
 compounds (see under "Determination of Silica," page 78). The 
 principle underlying this method is as follows: 
 
 All carbonates and all sodium salts are decomposed by strong 
 acids. When a compound is heated with sodium carbonate, at 
 the temperature of fusion, the constituents are transposed in such 
 a manner as to render them soluble, carbonates of the metals of 
 the compound are formed and the acid radicals combine with the 
 sodium. Since all carbonates and all sodium salts are decomposed 
 by strong acids, the originally insoluble compounds have been 
 changed into soluble forms. The reactions on page 78 show what 
 happens upon the decomposition of a silicate which may be taken 
 as a type of such a refractory substance. 
 
 REAGENTS 
 
 After getting the original substance into solution, the charac- 
 teristics of reagents selected to cause precipitation should be 
 considered. 
 
 A reagent is used which gives a definite and completely insoluble 
 compound with the element to be determined. For instance,
 
 18 QUANTITATIVE ANALYSIS 
 
 sulfuric acid could not be employed to determine calcium altho 
 it gives a precipitate of calcium sulfate in a fairly strong solu- 
 tion. Calcium sulfate is somewhat soluble and consequently an 
 oxalate which gives a completely insoluble compound is always 
 used. 
 
 Reagents most often employed are acids, their sodium or am- 
 monium salts, or alkalies. As they are readily soluble this makes 
 easy the preparation of their solutions for reagents. As a soluble 
 salt or acid results from the metathetical reaction with the com- 
 pound containing the element to be precipitated, most of it passes 
 into the filtrate and what is left may easily be washed from the 
 precipitate. 
 
 To illustrate: 
 
 Soluble Precipitate 4 
 
 FeCl 3 + 3 NH40H = 3 NH 4 C1 + Fe(OH) 3 
 and 
 
 Soluble Precipitate 
 
 BaCl 2 + H 2 S0 4 = 2 HC1 + BaSO. 
 
 Other compounds than the soluble salts and acids used for pre- 
 cipitations must be intelligently selected with the foregoing facts 
 in mind. 
 
 PRECIPITATION 
 
 It is evident that to completely separate one element from one 
 or more others in the same solution, a sufficient amount of a 
 reagent must be added to precipitate in an insoluble form all of 
 the given element, which may then be filtered off from the simul- 
 taneously occurring substances in the solution. It is not always 
 possible to form a precipitate entirely free from other compounds. 
 In such cases, subsequent purification is resorted to (see " Deter- 
 minations of Calcium and of Silica " for two types of such proced- 
 ure). When working with substances of known composition, as with 
 alum in the first determination, it is easy to calculate the amount 
 of reagent required. This is not often possible, since the composi- 
 tion of the substance and amount of each element present is un- 
 known. Generally, therefore, the reagent, which should always 
 be hot when conditions permit, is added slowly with constant 
 stirring of the solution until no further precipitate forms. This 
 point may be determined by letting the precipitate settle and 
 noting whether a few more drops of the reagent produce any
 
 GRAVIMETRIC ANALYSIS 19 
 
 precipitate in the clear, supernatant liquid. Filtrates always 
 should be re-tested for complete precipitation. 
 
 To be properly done, in Quantitative Analysis, precipitation re- 
 quires a good, clear knowledge of solubilities, both the solubility 
 of the substance in the liquid used and the solvent action of sub- 
 stances simultaneously formed should be considered (for example, 
 see the precautions necessary for the precipitation of calcium in 
 the presence of magnesium, pages 73 and 74). 
 
 A study of precipitation, then, the process of making insoluble 
 compounds, involves knowledge of the facts underlying the 
 phenomena of solution. 
 
 IMPORTANT FACTS ABOUT SOLUTIONS* 
 
 1. Conditions being the same, a great variation is noticed in the 
 solubility of different solids in the same liquid. 
 
 2. No solid is absolutely insoluble. Even barium sulfate dis- 
 solves to the extent of 1 part in 400,000 parts of water. 
 
 3. Heat generally aids solution. A few exceptions to this rule 
 are noted. Calcium citrate is more soluble hi cold water than in 
 hot water. Sodium chlorid, however, is about as soluble in cold 
 as in hot water. Heat is an aid to the solution of metals and 
 minerals in acids. 
 
 4. Water is the most universal solvent and has some solvent 
 action on almost everything. As previously stated, a solvent 
 must be selected to suit the individual case. No general rule can 
 be given. It should be remembered that the use of a concentrated 
 acid often appears to fail to give solution because the compounds 
 formed are not soluble in strong acid. Later dilution will often 
 cause complete solution. Even with a somewhat soluble com- 
 pound, a saturated solution may result and more water be needed 
 to destroy the saturated condition. 
 
 5. Dissolved substances tend to distribute themselves evenly 
 throughout the solvent but the process is slow and should be aided 
 by stirring or shaking. This is particularly to be observed in 
 making standard solutions. 
 
 * See "McPherson and Henderson" and other larger works for elaboration of 
 some of these facts.
 
 20 QUANTITATIVE ANALYSIS 
 
 6. All substances whose solutions conduct the electric current 
 dissociate when they dissolve in water. That is, the molecule 
 splits into two or more parts called ions which are as free to 
 move about in the solution as are independent molecules. These 
 ions carry electrical charges and hence differ in their properties 
 from the atoms or molecules. (See under " lonization," page 85.) 
 
 7. The equilibrium between substances in solution may be dis- 
 turbed and a reversible reaction may go to completion in three 
 ways: 
 
 (a) A gas may form and escape from the solution. 
 
 (b) An insoluble solid may form. 
 
 (c) Two different ions may form undissociated molecules. 
 
 8. Section (b) in the foregoing paragraph governs the phenom- 
 ena of precipitation as follows: 
 
 If HC1 and AgNO 3 are brought together in solution the following 
 ions will be present H + , Cl~, Ag+, NO^". The ions Ag + and Cl~ 
 will then set up the equilibrium 
 
 Silver chlorid is almost completely insoluble in water and the 
 formation of very little of it causes a supersaturated solution and 
 the excess of the salt precipitates. More ions of silver and chlorin 
 then unite until all have been removed from solution. 
 The following reaction is then complete: 
 
 AgN0 3 + HC1 = AgCl + HN0 3 . 
 
 The table on page 21 will give the student a knowledge of 
 solubilities of common compounds.
 
 GRAVIMETRIC ANALYSIS 
 
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 22 QUANTITATIVE ANALYSIS 
 
 HI. Filtering and Washing 
 
 These are the two most tedious processes of Analytical Chemis- 
 try. Altho it is possible by suitable care to hasten them, they 
 should not be slighted. They are facilitated by the use of well- 
 made funnels, accurately fitted filter papers and, in some cases, 
 by the use of suction. At best, however, they are both time 
 consuming and whenever possible should be carried on simulta- 
 neously with other work. 
 
 As small a filter paper as the amount of precipitate will allow 
 should be used. To wash a small amount of precipitate spread 
 out over the paper requires an unnecessarily large amount of 
 water, which should be avoided. The paper should not extend 
 above the edge of the funnel and should preferably come only 
 within one-fourth of an inch of its top edge. 
 
 It is desirable to carry on as many filtrations as possible at the 
 same time. A number of these will not require much more time 
 than a few. Filtration should be started as soon as possible after 
 the beginning of the laboratory period in order that it may be 
 finished at the end. It should be kept in mind that washing can- 
 not be finished if the precipitate has been allowed to stand any 
 length of time in an incompletely washed state. This is par- 
 ticularly true of gelatinous precipitates such as the hydroxids of 
 aluminium and iron, which dry rather quickly and form a non- 
 porous, film-like mass. Such dried precipitates inclose perma- 
 nently any soluble salts which might have been left in them. 
 Unless such salts happen to be volatile they still remain after the 
 ignition of the precipitate, whose weight they increase and cause 
 a consequent error in the result. It is evident that it is just as 
 fatal to accurate results to leave in the mass of the precipitate 
 any substance which should be washed away as to fail to obtain 
 all of the element sought. 
 
 The precipitate, then, should be perfectly washed and, in order 
 to prove that it is washed, the last few drops of the nitrate
 
 GRAVIMETRIC ANALYSIS 23 
 
 should be tested for some ingredient known to have been present. 
 Strangely enough this step is often ignored by beginners. Any 
 constituent known to have been in the filtrate may be the one 
 tested for. If an acid or alkaline solution is being filtered it 
 is customary to use the simple litmus paper test. This is not 
 only a delicate test but is also advantageous in that the litmus 
 paper can be washed off and the loss of the tested drop 
 avoided. 
 
 If the filtrate is to be used for the analysis of some other sub- 
 stance, only the fewest possible number of drops should be used 
 when testing for complete washing. Such tests should not be made 
 until it is fairly certain that the washing is complete so that the 
 loss of any considerable quantity of the substance in the filtrate 
 may be avoided. In other words, the filtrate should not be used 
 for testing for complete washing until it is probable that the 
 liquid is wash water only or an extremely dilute solution. 
 
 WASH WATERS 
 
 It is important that no more wash water be used than is abso- 
 lutely necessary to remove that which does not belong to the pre- 
 cipitate. When the filtration is sufficiently advanced, the filtrate 
 should be frequently tested both to save time and to avoid un- 
 necessary washing. Too much washing (1) wastes time, (2) 
 n dlessly increases the volume of the filtrate and (3) as no sub- 
 stance is entirely insoluble if treated with a sufficient volume of 
 water, tends to dissolve some of the precipitate. 
 
 Repeated treatments with small amounts of wash water give 
 better results than the addition of all the water at once; that is, 
 in washing a precipitate it is more advantageous to wash "by 
 decantation" ten times with a little of the wash water each time 
 than to wash once only with the total amount used in the successive 
 volumes. 
 
 Hot water ordinarily is better than cold. It runs through the 
 filter more quickly and is more efficacious in removing the sub- 
 stance to be washed out. 
 
 In order either to avoid the dissolving of some substance in 
 water or to increase the solubility of the substance to be removed, 
 special wash waters are often used. These are commonly dilute
 
 24 QUANTITATIVE ANALYSIS 
 
 acids, sometimes dilute alkali and, occasionally, such mixtures as 
 alcohol, ammonia and water or acidified solutions of salts such 
 as ammonium nitrate. 
 
 EVAPORATION OF LIQUIDS 
 
 Filtrates, owing to the volume of wash water used, are often 
 much too dilute. For this and for other reasons, such as the 
 necessity of boiling out an excess of volatile alkali or acid, it is 
 often necessary to boil down liquids which later are to be treated 
 quantitatively. It is obvious that any liquid which spatters out 
 removes with it a certain amount of the solids in solution, a loss 
 that later causes a lowering of the per cent, of the substance deter- 
 mined. Too rapid boiling is therefore inadvisable. 
 
 If simply the evaporation of the water in the filtrate is the object, 
 the beaker should be covered with a watch glass (sitting upon a 
 glass triangle) and should be allowed to evaporate slowly at a tem- 
 perature just below that of ebullition. If a solid is suspended hi 
 the liquid to be evaporated, still greater care should be exercised. 
 Steam forms in the mass of the solid and, upon expanding, forces it 
 violently upwards, giving rise to what is known as "bumping," 
 which is very likely to cause a loss. 
 
 Evaporations, if done directly above the lamp, should be carried 
 on over a moderate flame. Preferably they should be done on a 
 gas or electric hot plate covered with a thin sheet of asbestos. 
 Still better would be the use of a steam hot plate or steam bath 
 upon which there is no possibility of ebullition and spattering and 
 which may be left running all night without danger of fire.
 
 GRAVIMETRIC ANALYSIS 25 
 
 IV. Ignition to a Stable Compound 
 
 Ignition in Analytical Chemistry is the process of heating a sub- 
 stance without allowing the direct access of the flame to the com- 
 pound heated. It is accomplished by at first heating the crucible 
 only hot enough to destroy the filter paper by dry distillation and 
 later by increasing the heat. If the precipitate is to be subjected 
 to the high temperature of the blast lamp, it will be mentioned in 
 the directions. 
 
 Hastening the process of ignition, which is a temptation, is un- 
 wise, as it is almost sure to make the result too low. 
 
 Ignition may or will be the cause of any or all of the following 
 changes: 
 
 (1) Water of composition or water mechanically held may be 
 evolved. 
 
 (2) The filter paper will distill. 
 
 (3) The carbon of the filter paper will oxidize. 
 
 (4) The composition of the precipitate may undergo a chemical 
 change, as: 
 
 CaC 2 4 + A = CaO + CO 2 + CO. 
 
 (5) The precipitate may be reduced as: 
 
 BaS0 4 + 2 C = BaS + 2 CO 2 . 
 
 (6) The precipitate may be oxidized as: 
 
 BaS + 20 2 = BaS0 4 . 
 
 A precipitate may or may not be changed upon ignition; if 
 changed, it must change completely to a definite new compound. 
 If an incomplete or indefinite reaction would take place during the 
 burning off of the filter paper or if something would be lost by 
 volatilization, ignition should be omitted and the precipitate 
 weighed upon a "tared" filter paper or upon an asbestos layer 
 ("felt") previously weighed in a Gooch crucible. In either of 
 these latter cases, the precipitate on the paper or asbestos should be 
 completely dried in an air bath and weighed without ignition.
 
 26 QUANTITATIVE ANALYSIS 
 
 V. Weighing the Element or Stable Compound 
 
 Repeated ignition, cooling and weighing eventually give two 
 nearly the same consecutive weights, called "constant weights." 
 Two or more consecutive weights do not constitute a constant 
 weight if there is a greater variation than three-tenths of a milli- 
 gram, 0.0003 gram. The completion of the process of igniting to 
 a stable compound is shown only when a constant weight has been 
 reached. 
 
 If a precipitate is hygroscopic, it is necessary to hurry the weigh- 
 ing that the water absorbed may not add to its weight. Before 
 the crucible is taken from the desiccator the larger units of the 
 weight of the crucible may be placed on the pan. Upon re- 
 weighing, all of the weights in the box used in the previous weigh- 
 ing may be first put into place and the weighing finished with the 
 rider.
 
 GRAVIMETRIC ANALYSIS 27 
 
 VI. Calculating the Per Cent, from Data Obtained 
 
 Sample calculations are given at the end of each new method if 
 there is any new principle involved. These serve only as a basis 
 upon which to work. Facility in calculation may be acquired by 
 an exhaustive variety of problems assigned by the Instructor or 
 taken from the following books: 
 
 Baskerville and Estabrook's "Chemical Problems." 
 
 Well's " Textbook of Chemical Arithmetic." 
 
 Hale's " Calculations of Chemistry." 
 
 Lupton's " Chemical Arithmetic." 
 
 The initial substance is weighed only to the fourth decimal place, 
 as, for example, 0.2343 gram. It is therefore futile in the various 
 steps of the calculation to use figures beyond the fourth decimal 
 place. In subtracting the ash, for instance, use the figures as 
 follows: 
 
 precipitate +ash = 0.1389 or ppt. +ash = 0.1389 
 
 ash= 0.00007 ash = 0.00014 
 
 precipitate = 0.13883, use 0.1388 ppt. = 0.13876, use 0.1388. 
 
 In calculating the results of analyses the use of logarithms is 
 to be preferred, not only because it saves time but also because of 
 the fewer figures employed there is much less possibility of error. 
 
 FACTORS 
 
 The element or compound isolated is not always weighed in the 
 form in which it is to be reported, as, for example, iron may be 
 weighed as ferric oxid, Fe 2 O 3 , and reported as per cent, of iron. 
 The relationshipjbetween the molecular weight of the element or 
 
 compound sought and the molecular weight of the "element or 
 Compound reported is expressed by a factor found by making a 
 proportion between the two. The factor used to change barium
 
 28 QUANTITATIVE ANALYSIS 
 
 sulfate, BaSO 4 , into terms of barium oxid, BaO, for instance, may 
 be found as follows: 
 
 BaSO 4 : BaO = Weight of the BaS0 4 : x. 
 BaO 
 
 BaS0 4 
 
 X Weight of BaSO 4 . 
 
 Molecular weight of BaO 153.4 . 
 
 Molecular weight of BaS0 4 " 233.5 " JaC 
 
 Therefore, weight BaO, or x = 0.6571 X weight of the BaS0 4 . 
 
 A table containing all the factors and their logarithms needed in 
 calculating the results of the analyses in this course may be found 
 on page 155.
 
 GRAVIMETRIC ANALYSIS 29 
 
 PLANNING THE WORK, ETC. 
 
 The student should particularly note that the one who accom- 
 plishes the most analytical work is he who plans in advance and 
 who carries on several processes at once. He reads ahead in the 
 directions and sees the place at which a wait is to occur, an 
 evaporation, a dehydration, etc., and makes sure that there is 
 some other work sufficiently advanced to at once occupy the time. 
 
 It is necessary to state that absolute cleanliness, nothing less, 
 must be observed. It will be mere luck if even fair results are 
 obtained under other conditions. A linen towel should be used 
 for the final wiping of all porcelain and glass ware. The free use 
 of labels bearing explicit statements is necessary if one is to avoid 
 error. Whenever possible, dishes should be covered with watch
 
 30 QUANTITATIVE ANALYSIS 
 
 NOTEBOOKS 
 
 Careless records of results are almost certain to bring disaster. 
 To eliminate this source of trouble, a notebook is a necessity. 
 
 The following directions are to be observed: 
 
 (1) Use the left-hand page for a re'sume' of the process and for 
 keeping a complete record of anything unusual that happens 
 throughout the entire analysis. 
 
 (2) Record weights always in ink directly into the book. Never 
 use loose bits of paper. 
 
 (3) On the first two analyses have each weight stamped 
 "CHECKED" by the Instructor.
 
 GRAVIMETRIC ANALYSIS 
 (4) Arrange the right-hand page as follows: 
 
 Determination of . 
 
 Analysis begun: date 
 Analysis ended: date 
 
 31 
 
 Charge 1 
 
 Weight of tube + substance = 
 
 Weight of tube charge = 
 
 Weight of charge = 
 
 Weight of crucible + precipitate + ash = 
 
 II U (( l( (( 
 
 Accepted constant weight of crucible 
 
 + precipitate + ash = 
 
 Weight of crucible = 
 
 Weight of precipitate -f- ash = 
 Weight of ash 
 Weight of precipitate = 
 
 . 1st heating, 
 . 2nd heating, 
 . 3rd heating, 
 .etc. 
 
 CALCULATION 
 
 (See sample calculations) 
 
 %of 
 
 (5) Make all the calculations in the book and, as before recom- 
 mended, use logarithms for calculations.
 
 32 QUANTITATIVE ANALYSIS 
 
 THE FACTS CONTAINED UNDER "APPARATUS" 
 AND "PROCESSES EMPLOYED IN GRAVIMETRIC 
 ANALYSIS" MUST HAVE BEEN LEARNED BE- 
 FORE WORK IN THE LABORATORY Is BEGUN. 
 
 BEFORE BEGINNING EACH NEW DETERMINA- 
 TION, IT Is ESSENTIAL FOR THE STUDENT BE- 
 FORE COMING INTO THE LABORATORY TO HAVE 
 STUDIED AND MASTERED THE PROCESS AND 
 ITS ACCOMPANYING NOTES.
 
 GRAVIMETRIC ANALYSIS 
 
 DETERMINATION OF ALUMINIUM 
 
 IN 
 POTASSIUM ALUM, KAl(SO 4 ) 2 .i2H 2 O 
 
 ALUMINIUM is: 
 
 (a) precipitated by ammonium hydroxid, NH 4 OH, as alumin- 
 ium hydroxid, A1(OH) 3 , in the presence of an ammo- 
 nium salt, NH 4 C1; 
 
 (6) converted by ignition to and weighed as aluminium oxid, 
 A1 2 3 ; 
 
 (c) calculated as per cent, of aluminium. 
 
 REACTIONS 
 
 I. 2 KA1(SO 4 ) 2 + 6 NH 4 OH = 2 Al(OH), 
 
 + 3(NH 4 ) 2 SO.j, 
 
 II. (2A1(OH) 3 +A = 2A1O(OH)+2H 2 0) 
 III. ( 2 AIO(OH) + A = A1 2 3 + H 2 0, 1 
 
 or 
 IV. 2 A1(OH) 3 + A = A1 2 O 3 + 3 H 2 O.
 
 34 QUANTITATIVE ANALYSIS 
 
 DETERMINATION OF ALUMINIUM 
 
 A rigid adherence to the minute directions given under "Alumin- 
 ium" will save time and will give skill in manipulation, an essential 
 to accurate results. 
 
 PROCEDURE 1 
 
 On a 350 c.c. beaker (No. 3), which should be covered with a 
 
 watch glass, place a label marked "Al." 
 Wipe off the cork and weighing tube containing the salt and 
 
 replace the cork. 
 Weigh the tube containing the salt and record the weight on the 
 
 right-hand page of the notebook. 
 Hold the weighing tube inclined slightly upwards over the mouth 
 
 of the beaker and carefully remove the stopper, which, to 
 
 prevent loss, is held over the dish. Tip 
 
 ' . Weighing the charge 
 
 the mouth of the tube downwards into 
 the beaker and with slight taps, or rotary motion, remove 
 from the tube an amount sufficient to make a charge of 
 about 1 gram 2 of the salt. Tap down into the tube what- 
 
 EXPLANATORY FACTS 
 
 1. As this is a salt of known composition, each student should 
 check his work by calculating the per cent, of aluminium in 
 KA1(SO 4 )2.12 H 2 O. This calculation must be put in full on the 
 left-hand page of the notes. 
 
 This determination is not done in duplicate. 
 
 2. AfeOs, the final substance weighed, is about only one- 
 ninth of the original charge. It is therefore desirable to start 
 with a somewhat large quantity.
 
 GRAVIMETRIC ANALYSIS 35 
 
 ever remains. Replace the cork and weigh again. At all 
 times, in order to avoid moisture from the hands, hold the 
 tube and cork as lightly as possible. 
 
 Record the weight under the first entry and subtract to get the 
 weight of the salt to be used for analysis. 
 
 Dissolve by pouring on the salt 100 c.c. of hot, Dissolving the sub- 
 distilled water. stance 
 
 PROCEDURE 
 Add 25 c.c. of a solution of ammonium* chlorid. 3 ** 
 
 EXPLANATORY FACTS 
 
 3. Metallic hydroxids are not completely precipitated in the 
 presence of tartaric and citric acids, sugar, etc. In such cases, 
 nonvolatile organic matter must be decomposed by adding 
 Na2COs and KNOs to the solution, evaporating to dryness, fusing 
 the residue and extracting it with dilute hydrochloric acid. 
 
 4. (a) The presence of the ammonium salts (1) insures the 
 complete precipitation of the aluminium hydroxid, Al(OH)s, since 
 such salts cause the reprecipitation of the A1(OH) 3 which might 
 be dissolved in the excess of the reagent and (2) affects the 
 physical state of the aluminium hydroxid by preventing the 
 formation of a colloidal or semisoluble condition (hydrosol). 
 Boiling alone does not completely change hydrosol into insolu- 
 ble hydrogel. 
 
 (6) It is usually observed that precipitates made from solutions 
 containing large quantities of ammonia salts will, when washed 
 with hot water, become sticky and wash so slowly that it is im- 
 possible to free them from the last traces of the salts and also that 
 very perceptible quantities of alumina settle out from such wash- 
 ings and filtrates. It is essential for successful precipitations to 
 avoid such excesses. 
 
 * "Chemistry of the Metals," Experiments Nos. 217 and 218.
 
 36 QUANTITATIVE ANALYSIS 
 
 Add perfectly clear ammonium hydroxid in slight 
 
 excess, 5 that is, until the odor persists after 
 
 the solution is stirred. 
 
 Cover the beaker with a watch glass and boil gently until the 
 
 odor of ammonia has nearly disappeared and until red 
 
 litmus paper held over the solution is only slowly turned 
 
 blue. 6 
 
 Rinse off the inside of the watch glass into the beaker by means 
 
 of a jet of hot water from the wash bottle. 
 While the precipitate is subsiding 
 
 Fold the filter paper exactly into quarters. 
 
 Open the paper into a cone and force it into the apex of the 
 
 funnel. 
 To complete the fitting process so that there shall be no air 
 
 spaces 7 between the glass and the paper, fill the funnel 
 
 with distilled water, let some of it run through the 
 
 stem, pour out the rest and, where it is necessary, 
 
 press the paper against the glass. 
 Place a larger beaker, one of 500 c.c. capacity (No. 4), on 
 
 a clean piece of filter paper on the base of the filter 
 
 stand. 
 Arrange the funnel so that its tip will come 
 
 just below the curve of the lip of the a J d n of the 
 
 beaker and touch its side. 
 
 EXPLANATORY FACTS 
 
 5. Aluminium hydroxid is soluble in an excess of ammonium 
 hydroxid.* 
 
 6. Upon long boiling, by decomposition of the salts, ammonia 
 is liberated and the solution becomes acid. 
 
 7. If an air space is left, it destroys the accelerating effect of 
 the weight of water in the long-stemmed funnel, the reason for 
 having a funnel with so long a stem. 
 
 * "Chemistry of the Metals," Experiment No. 217.
 
 GRAVIMETRIC ANALYSIS 37 
 
 Without delay 8 pour off the supernatant liquid into the filter as 
 follows: 
 
 To avoid spattering, pour down a stirring rod held against 
 the lip of the beaker, so that the stream of liquid will 
 strike the doubled side of the filter paper, not upon the 
 surface of the solution hi the funnel. The level of the 
 liquid should be kept an eighth of an inch below the edge 
 of the paper. 
 
 The entire contents of the funnel should be allowed to run 
 out before more is added. In the long run this saves 
 time. 
 
 The mistake should not be made of transferring at the start 
 much, if any, of the precipitate. It should be allowed to 
 settle completely in the beaker and the supernatant liquid, 
 only, be decanted off through the filter paper. 
 Wash the precipitate in the beaker by decanta- Washing a^ hy _ 
 
 tion 9 With hot Water. 10 This is aCCOm- droxid by decanta- 
 
 plished as follows: 
 
 Direct carefully down the rod or sides of the beaker a 
 stream of hot, distilled water from the wash bottle 
 into the precipitate. Stir with a rounded glass rod 
 and allow the precipitate to settle. Pour off the water 
 through the filter. 
 This washing, settling and filtering should be done three 
 
 times. 
 During filtration save time by igniting the crucible according 
 
 to the directions given on pages 39 and 40. 
 
 EXPLANATORY FACTS 
 
 8. Ammoniacal liquids exert a solvent action upon glass. 
 
 9. By decantation, a precipitate is washed more thoroughly 
 and in less time than if transferred at once to the filter paper and 
 entirely washed in the funnel. 
 
 10. It is sometimes advantageous to have added to the hot 
 water two drops of ammonium hydroxid and two grams of am- 
 monium nitrate per liter (see fact 4 (6)).
 
 38 QUANTITATIVE ANALYSIS 
 
 As quickly as possible, 11 transfer the precipitate quantitatively 
 to the filter paper. Hold the beaker in the left hand using 
 the forefinger to keep in place the stirring rod which should 
 rest across the top of the beaker, one end touching and 
 extending beyond the lip. With the right forefinger on the 
 movable tip of the wash bottle, direct the stream of water 
 hi such a manner as to wash the precipitate from the beaker 
 down the stirring rod into the funnel. When the precipitate 
 is apparently removed, rub the stirring rod clean with the 
 "policeman" or with a closely trimmed goose quill and hot 
 water from the wash bottle. Rub the entire surface of the 
 beaker with the "policeman" aided by a fine stream of hot 
 water. Pour this liquid into the filter. Finally, closely 
 scrutinize the beaker held hi a strong light to be sure that 
 it is perfectly clean on the inside. Wash off into the filter 
 any precipitate that may remain on the "policeman." 
 Wash the precipitate hi the funnel with hot water as follows: 12 
 Direct the stream of water against the double fold of the 
 paper and then, with a rotary motion of the wash- 
 bottle tip, bring the jet of water out into the mass of 
 the precipitate. Let drain and repeat, washing the h y - 
 Before the filtrate is tested for com- drraid ' m * fmmel 
 plete washing, the upper edges of the paper should be 
 washed with extreme care. Avoid getting any of the 
 precipitate above the paper level. 
 
 EXPLANATORY FACTS 
 
 11. If not done at once, the precipitate will adhere to the 
 beaker and be removed with difficulty. 
 
 12. Aluminium hydroxid soon hardens and cracks and there- 
 fore should at once be washed completely. Filtration once begun 
 must be finished during the laboratory period.
 
 GRAVIMETRIC ANALYSIS 39 
 
 Test a few drops of the filtrate with silver nitrate* solution for 
 chlorids. 13 The precipitate must be washed till a fresh por- 
 tion of the filtrate gives no evidence of Testing the filtrate for 
 their presence. As stated above, never complete washing 
 completely fill the filter and never add more liquid till the 
 filter has entirely drained. 
 
 Test the filtrate with a little more ammonium hydroxid to insure 
 complete precipitation. 
 
 Cover the funnel with an ordinary 11 cm. filter paper wet with 
 distilled water. Stretch it over the top by pressing the 
 projecting run of the paper firmly around the outside of the 
 funnel. Tear off the extra paper which hangs below the 
 edge. Enough will remain to hold it on. 
 
 Place the covered funnel in an air bath to dry the precipitate. 
 It is possible, with great care, to ignite the precipitate with- 
 out drying, but it introduces a greater Drying the pre- 
 chance of error. It is much better to ci P ita t 
 proceed with other work and return to this when it has 
 dried. 
 
 Wash either a platinum or a porcelain crucible thoroughly and 
 dry with an "analytical" towel (pure linen). With a pair 
 of nickel tongs, place the crucible upon a clean pipestem 
 triangle. 
 
 EXPLANATORY FACTS. 
 
 13. The reaction at the beginning of this analysis shows the 
 formation of K 2 S0 4 and (NH^SO*. These and also the added 
 NHiCl should be completely removed to avoid increasing the 
 weight of aluminium hydroxid. When the absence of chlorids 
 is assured, it may be assumed that the two sulfates are also 
 removed. 
 
 * "Chemistry of the Metals," Experiment No. 49.
 
 40 QUANTITATIVE ANALYSIS 
 
 For a few minutes, heat the partially covered crucible to redness 
 with a properly adjusted Bunsen flame. Remove the Bun- 
 sen. After the redness has died down, with the tongs put 
 the crucible and cover in to the desiccator to cool. On the 
 porcelain plate, next to the hole holding the crucible, there 
 should be pasted a label marked "Al." 
 
 After twenty minutes, weigh the crucible and weighing the 
 cover, replace them in the desiccator and crucible 
 record the weight. 
 
 When the precipitate is dry, leave the cover in the desiccator 
 and put the crucible on a piece of glazed paper. Neither 
 crucible nor cover after having been weighed should be put 
 anywhere but on the desiccator plate, the triangle, glazed 
 paper or on a clean watch glass. 
 
 Remove the filter paper from the funnel, fold it carefully and 
 place it with its contents in the base of the crucible. This 
 is not the type of precipitate which is reduced by the 
 carbon of the filter paper; they may, therefore, be ignited 
 together. 
 
 If any of the precipitate adheres to the funnel, wipe it off on a 
 small bit torn from the clean, folded portion of the filter 
 paper and put it into the crucible with the main precipitate. 
 
 Place the crucible at an angle on the triangle on the lamp stand. 
 
 If the dried filter paper is charred with great care, there is no 
 danger of mechanical loss. If, however, for any reason, the 
 precipitate is wet or moist, the crucible should be placed 
 upright and the utmost pains taken not to heat it suffi- 
 ciently to cause a violent escape of steam, which might 
 drive out some of the precipitate. The ring of the stand 
 should be so adjusted as to bring the crucible above but 
 not touching the flame. When the paper has dried, the 
 crucible may be turned on its side. 
 
 Too much care cannot be exercised at this point. The object 
 is to destroy the filter paper by dry distillation and not to 
 burn it. Avoid future difficulty by implicitly following 
 these directions. It is possible to place the crucible at 
 such a distance above the flame as to accomplish this end. 
 It is, however, advisable to stand at the work, lamp in 
 hand, with a low flame, ready to withdraw it if the escape
 
 GRAVIMETRIC ANALYSIS 41 
 
 of volatile matter becomes too violent. If, through the in- 
 experience of the student, the paper takes igniting the 
 fire, the tongs should be at hand that the precipitate 
 lid may be taken from the desiccator and the crucible 
 covered to extinguish the flame. After the escape of 
 vapors has ceased and the filter paper has completely 
 charred, the heat may be increased and the charred paper 
 ignited till the carbon is oxidized. 
 
 Heat ten minutes over the blast lamp. 14 
 
 Remove the crucible to the desiccator, the cover of which should 
 be put on with a slight twist, and cool until the crucible has 
 acquired the temperature of the room. A red-hot crucible 
 should not be placed in the desiccator. No great time, 
 however, must elapse between the removal of the lamp and 
 the insertion of the crucible. If the crucible is put in hot 
 enough to expand the air and to lift the cover of the desic- 
 cator, the cover should be carefully readjusted. 15 Three 
 facts should be borne in mind: (1) The desiccator always 
 should be kept covered, except at the moment of putting 
 in or taking out the crucible, which, after ignition, should 
 never be handled except with the tongs. (2) The cover 
 of the desiccator unless inverted should never be put down 
 on anything but the desiccator itself. (3) Before weighing, 
 the desiccator and its contents should be put either in the 
 balance room or in a place in which it will acquire the 
 approximate temperature of the balance- 
 
 EXPLANATORY FACTS 
 
 14. The final ignition in the blast lamp is to expel the last 
 traces of water and insure complete change to oxid (see reactions 
 II and III). 
 
 15. Carefully, because this expansion of the air may have pro- 
 duced a reduced pressure, and the inrush of air may cause some 
 of the precipitate to fly out of the crucible.
 
 42 QUANTITATIVE ANALYSIS 
 
 Weigh 16 and record Weights. Weighing the ignited 
 
 Repeat heating over blast lamp, cooling and p feci P itate 
 
 weighing till the weights agree within three-tenths of a 
 milligram. This will bring the substance to a "constant 
 weight." 
 
 EXPLANATORY FACTS 
 
 16. Aluminium oxid is hygroscopic and should, therefore, be 
 weighed quickly.
 
 GRAVIMETRIC ANALYSIS 43 
 
 SAMPLE CALCULATION 
 
 Weighing tube and salt = 6.0227 grams 
 Weighing tube charge = 4.9666 grams 
 Weight of charge = 1.0561 grams 
 
 Weight of crucible + ash + A1 2 3 = 11.9108 grams 
 Weight of crucible = 11.7973 grams 
 
 Weight of ash and A1 2 O 3 = 0.1135 gram 
 
 Weight of ash = 0.0001 gram 
 
 Weight of A1 2 O 3 = 0.1 134 gram 
 
 Atomic weight of Al = 27.10 
 
 " = 16 
 
 Molecular weight of A1 2 = 54.20 
 " A1 2 3 = 102.20 
 
 The ratio of A1 2 to A1 2 O 3 = = 0.53033. 
 
 0.53033 is the constant factor that represents the amount of Al 
 in A1 2 O 3 . 
 
 (Weight of A1 2 O 3 ) 0.1134 gram multiplied by 0.53033 (the con- 
 stant factor) = 0.06013 gram of Al in 0.1134 gram of A1 2 O 3 . 
 
 Since there is 0.06013 gram of Al in the original charge of 1.0561 
 of the salt, then: 
 
 0.06013 X 100 _ ftoc/ A1 
 -L0561 - = 5 ' 69%AL
 
 44 
 
 QUANTITATIVE ANALYSIS 
 
 CALCULATION BY LOGARITHMS 
 
 The logarithm of the weight of A1 2 C>3 minus the logarithm of the 
 weight of the original charge plus the logarithm of the constant 
 factor of the amount of Al in A1 2 O 3 equals the logarithm of the 
 per cent, of Al. 
 
 Log. of (weight of A1 2 O 3 ) 0.1134 = 9.05461-10 
 Log. of (original charge) 1.0561 = 0.02366 
 
 9.03095-10 
 Log. of (constant factor) 0.53033 = 9.72454-10 
 
 18.75549-20 or 
 2.75549 
 
 Anti-log, of 2.75549 = 0.0569 or 5.69 % Al.
 
 GRAVIMETRIC ANALYSIS 45 
 
 THE DETERMINATION OF COPPER 
 
 IN 
 PURIFIED COPPER SULFATE, CuSO 4 .5H 2 O * 
 
 Copper is: 
 
 (a) precipitated by sodium hydroxid, NaOH, as cupric hy- 
 
 droxid Cu(OH) 2 ; 
 (6) converted by boiling and ignition to cupric oxid, CuO, a 
 
 type of precipitate that must be largely removed from 
 
 the filter paper before ignition; 
 
 (c) weighed as cupric oxid; 
 
 (d) calculated as per cent, of copper. 
 
 REACTIONS 
 
 I. CuSO 4 + 2 NaOH = Cu(OH) 2 + NaSO4. 
 II. Cu(OH) 2 + A = CuO + H 2 0. 
 
 III. CuO + C = Cu + CO. 
 
 IV. 3 Cu + 8 HNO 3 = 3 Cu(NO 3 ) 2 + 4 H 2 O + 2 NO. 
 V. 2 Cu(N0 3 ) 2 + A = 2 CuO + 4 N0 2 + O 2 . 
 
 * If this course is to be limited to ninety hours, the determination of copper may 
 be omitted. Otherwise, the value of the preparation of a pure from a commercial 
 salt and the practice of the separation of a precipitate from the filter paper before 
 ignition justify the time expended.
 
 46 QUANTITATIVE ANALYSIS 
 
 PREPARATION OF THE PURE CuSO 4 .5H 3 O FROM 
 " BLUE VITRIOL (COMMERCIAL) 
 
 Weigh 50 grams of commercial copper sulfate on a rough balance. 
 
 Dissolve by heating in 150 c.c. of distilled water. 
 
 Add 1 c.c. of dilute nitric acid 17 and keep the solution boiling 
 
 gently for fifteen minutes. 
 Filter and put the beaker containing the filtrate in cold water. 
 
 Stir vigorously to get finely divided crystals. 
 Filter, wash the crystals with a small amount of cold water, let 
 
 drain and dry by pressing gently 18 between a folded sheet 
 
 of filter paper. 
 Put the crystals on a clean five-inch watch glass and let dry in 
 
 the open air. Turn the crystals over frequently with a 
 
 clean stirring rod until they no longer adhere to the 
 
 Transfer the crystals at once to a piece of glazed paper creased 
 through the middle and empty into a test tube that has 
 been fitted with a cork. 
 
 EXPLANATORY FACTS 
 
 17. Commercial "blue vitriol" usually contains ferrous sulfate. 
 Ferrous sulfate and copper sulfate tend to crystallize together and 
 cannot, therefore, be separated by "fractional crystallization." 
 The ferrous sulfate is consequently oxidized to ferric sulfate by 
 the nitric acid. The ferric sulfate does not tend to separate 
 with the copper sulfate which is easily obtained in crystals after 
 concentrating the liquid. 
 
 18. If pressed roughly, fragments of the paper may mix with 
 the crystals.
 
 GRAVIMETRIC ANALYSIS 47 
 
 PROCEDUBE * 
 
 Fill a weighing tube two-thirds full of the purified copper 
 
 sulfate l9 and fit in a cork. 
 Weigh into a 250 c.c. casserole, labeled "Cu," 
 
 , ' Weighing the charge 
 
 one gram of the salt and record the 
 weight. 
 Dissolve in 100 c.c. of hot, distilled water. Dissolving the 
 
 The solution should be perfectly clear. substance 
 Cover the beaker and heat the solution to boiling f (see reac- 
 tion II). 
 
 While stirring with a glass rod having rounded Precipitation of the 
 ends, add, drop by drop, a dilute solution of hvdroxid 
 sodium hydroxid 20 (see reaction I) hi slight excess. 21 
 Stir constantly and continue to heat for ten minutes. Keep the 
 beaker covered when possible. 
 
 Test for excess of sodium hydroxid by putting a drop of the 
 solution on a strip of red litmus paper with the stirring rod. 
 Wash off the litmus paper into the beaker with a little distilled 
 water from the wash bottle. 
 
 EXPLANATORY FACTS 
 
 19. As this is a salt of known composition, each student must 
 check his work by calculating the per cent, of copper in 
 CuSO4.5H 2 O. This calculation should be put on the left-hand 
 page of the note-book. 
 
 20. When cupric hydroxid is first formed it is a greenish blue; 
 it turns brown at once at a boiling temperature and then nearly 
 black. This indicates the change to cupric oxid. 
 
 21. Cupric hydroxid is insoluble in excess of fixed alkalies in 
 dilute solution. 
 
 * This determination is not done in duplicate. 
 
 t See "Chemistry of the Metals," Experiment No. 102.
 
 48 QUANTITATIVE ANALYSIS 
 
 Rinse off the underside of the watch glass into the beaker by 
 means of a jet of hot water from the wash bottle. 
 
 While the precipitate is settling, fit a filter paper (S. & S. "Ash- 
 less," 11 cm.) hi to a funnel as described on page 36. To 
 collect the filtrate, use a 500 c.c. beaker (No. 4). 
 
 After the precipitate has settled, pour off the Filtration of the 
 liquid through the filter. oxid 
 
 Carefully direct a stream of hot water from the 
 
 Washing the oxid 
 
 wash bottle into the precipitate and stir. 
 
 Boil again. 22 
 
 Wash by decantation several times, page 37. 
 
 During filtration, start the heating, cooling and Preparation of the 
 weighing of the porcelain crucible, page 39. crucible 
 
 Transfer the precipitate quantitatively to the filter paper as 
 described in detail under "The Determination of Alu- 
 minium," page 38. 
 
 Wash the precipitate in the funnel with hot water until a few 
 drops of the filtrate acidified with hydrochloric add give 
 with barium chlorid solution no test for sul- Testing ^ si^te 
 fate.* Direct the stream downwards onto for complete 
 the upper part of the filter. As previously washmg 
 stated, never completely fill the filter paper and wait till it 
 has entirely drained before adding more liquid. 
 
 Cover the funnel with an ordinary 11 cm. filter paper wet with 
 distilled water. 
 
 Place the funnel hi an oven to dry the precipi- Drying of the 
 
 tate. precipitate 
 
 This precipitate cannot be ignited with the paper as the carbon 
 from the filter paper will reduce copper oxid to metallic 
 copper (see reaction III). 
 
 EXPLANATORY FACT 
 
 22. Cupric hydroxid must be completely changed by boiling to 
 cupric oxid. 
 
 * See "Chemistry of the Metals," Experiment No. 232.
 
 C 
 
 GRAVIMETRIC ANALYSIS 49 
 
 Place a perfectly clean three-inch watch glass upon a circular 
 piece of glazed paper about six inches in diameter. 
 
 Separate the copper oxid from the filter paper in the following 
 manner: Remove the filter paper from the funnel. Gently 
 loosen the precipitate adhering to the sides of the paper by 
 pressing the funnel-shaped paper with Separatioa of ^ 
 thumb and fingers. With great care empty copper ond from the 
 the bulk of the contents of the filter paper mter **" 
 upon the watch glass. Invert the filter paper over the 
 watch glass and gently rub the sides together. Avoid 
 rubbing hard enough to detach threads of the paper. 
 Cover the precipitate with an inverted six-inch watch 
 glass. 
 
 Wipe off any of the precipitate that has adhered to the glass 
 funnel and drop the bit of paper into the filter-paper 
 cone. 
 
 Fold the filter paper, which should be flattened into the shape 
 of a quarter circle, in halves lengthwise, fold once more in 
 the same way. Roll the top edge and secure it by 
 fastening around it loosely a platinum wire which will 
 then come into contact with clean paper 
 
 Preparing and burning 
 Only. the filter paper after 
 
 Hold the folded filter paper by the wire over 
 
 the weighed crucible, which should stand 
 
 on a piece of glazed paper. Burn and let the ash fall into 
 
 the crucible (see reaction III). 
 Moisten the residue with one or two drops of nitric add to dis- 
 
 solve it and form cupric nitrate * (see Treatment of any 
 
 reaction IV). reduced oxid 
 
 To avoid loss by spattering, heat with great care on a hot plate 
 
 to drive off the excess of nitric acid till the mass is dry (see 
 
 under "Evaporation of Liquids," page 24). 
 Place the crucible on its side on a clean, clay triangle on a 
 
 ring stand and heat first gently and then to redness till the 
 
 cupric nitrate has changed into black cupric oxidf (see 
 
 reaction V). 
 
 * See "Chemistry of the Metals," Experiment No. 91. 
 t See "Chemistry of the Metals," Experiment No. 96.
 
 50 QUANTITATIVE ANALYSIS 
 
 Remove the lamp and when the crucible is nearly cool, place 
 it on a piece of glazed paper and transfer the main part of 
 the precipitate which is on the watch glass into the crucible. 
 Brush off the particles remaining on the Treatment of ^^ 
 glass with a small brush or trimmed entire combined 
 feather. Finally brush into the crucible precipltate 
 any particles that may be on the glazed paper. 
 Heat strongly for a few more minutes. ignition 
 
 Cool in the desiccator. cooling, and 
 
 Weigh and record the weight. weighing 
 
 Repeat the heating, cooling and weighing till 
 
 the weights agree within three-tenths of a milligram, thus 
 bringing the substance to a "constant weight."
 
 GRAVIMETRIC ANALYSIS 51 
 
 SAMPLE CALCULATION 
 
 The per cent, of Cu in CuS0 4 .5 H 2 O. 
 
 Weighing tube + copper sulfate = 14.8345 grams 
 Weighing tube charge = 13.6405 grams 
 
 Weight of charge = 1.1940 grams 
 
 Weight of crucible with cover + ash -f CuO = 25.4987 grams 
 Weight of crucible with cover = 25.1190 grams 
 
 Weight of ash and CuO = 0.3797 grams 
 
 Weight of ash = 0.0002 grams 
 
 Weight of CuO = 0.3795 grams 
 
 Atomic weight of Cu = 63.60 
 
 " " O =16.00 
 
 Molecular " " CuO = 79.60 
 
 The ratio of Cu to CuO =' = 0.79897 + or 0.7990. 
 
 0.7990 is the "constant factor" that represents the amount of 
 Cu in CuO. 
 
 (Weight of CuO), 0.3795 grams, multiplied by 0.7990 (the con- 
 stant factor) = 0.30322 gram of Cu in 1.1940 grams of the salt. 
 
 0.30322^ 100
 
 52 QUANTITATIVE ANALYSIS 
 
 CALCULATION BY LOGARITHMS 
 
 The logarithm of the weight of CuO minus the logarithm of the 
 weight of the original charge plus the logarithm of the constant 
 factor of the amount of Cu in CuO equals the logarithm of the per 
 cent, of Cu. 
 
 Log. of (weight of CuO) 0.3795 = 9.57921-10 
 Log. of (original charge) 1.1940 = 0.07700 
 
 9.50221-10 
 Log. of (constant factor) 0.79900 = 9.90255-10 
 
 19.40476-20 or 
 1.40476 
 
 Anti-log of 1.40476 = 0.2539 or 25.39%.
 
 GRAVIMETRIC ANALYSIS 53 
 
 DETERMINATION OF IRON 
 
 IN AN 
 
 UNKNOWN, SOLUBLE, FERROUS SALT SIMILAR TO 
 FERROUS SULFATE 
 
 Iron is: 
 
 (a) oxidized in the presence of hydrochloric acid to the ferric 
 
 state by nitric acid, HNO 3 ; 
 (6) precipitated by ammonium hydroxid, NH 4 OH, as ferric 
 
 hydroxid, Fe(OH) 3 ; 
 
 (c) converted by ignition to, and weighed as, ferric oxid, Fe 2 O 3 . 
 
 (Type of precipitate which by ignition loses component 
 water) ; 
 
 (d) calculated as per cent, of iron. 
 
 REACTIONS 
 
 I. 6FeS0 4 + 8HNO 3 = 2Fe 2 (SO 4 ) 3 + 2Fe(NO 3 ) 3 + 2 NO 
 
 + 4H 2 O. 
 II. 2 FeS0 4 + NO = (FeS0 4 ) 2 NO. 
 
 III. Fe 2 (S0 4 ) 3 + 6 NH 4 OH = 2 Fe(OH) 3 + 3 (NH 4 ) 2 SO 4 . 
 
 IV. Fe(N0 3 ) 3 + 3NH 4 OH = Fe(OH) 3 + SKH^Os. 
 V. 2 Fe(OH) 3 + A = F^O 3 + 3 H 2 O. 
 
 ADDITIONAL REACTIONS POSSIBLE IN THE PROCESS 
 
 VI. 2 FeSO 4 + O = Fe2O(SO 4 ) 2 . 
 
 VII. 3 Fe 2 0(S0 4 ) 2 + 6 HC1 = 2 Fe 2 (SO 4 ) 3 + 2 FeCla + 3 H 2 0. 
 VIII. 3 FezOs + C = CO + 2 Fe 3 O 4 . 
 IX. 2Fe 3 4 + O = 3Fe 2 3 . 
 
 X. Fe(OH) 3 + 3 NH 4 C1 + A = FeCl 3 (partly volatile) 
 
 + 3NH 3 + 3H 2 O.
 
 54 QUANTITATIVE ANALYSIS 
 
 DETERMINATION OF IRON 
 
 PROCEDURE 
 
 Weigh into two 350 c.c. beakers (No. 3), two weighing the 
 
 portions of the salt of 1.5 grams each. charge 
 
 Dissolve in 100 c.c. of distilled water to which Dissolving the 
 
 4 c.c. of concentrated hydrochloric* add 23 substance 
 
 have been added. 
 Cover the beakers with watch glasses, bring the oxidizing the iron 
 
 solution to a boil and add to each 2 c.c. of to *" ferric state 
 
 nitric f aa'd. 24 * 25 
 Again cover the beakers and keep them at the boiling point for 
 
 about fifteen minutes. The solutions will now show the 
 
 presence of ferric salts by the clear yellow or red color 
 
 EXPLANATORY FACTS 
 
 23. Unless there is free acid present, ferrous iron will not 
 wholly oxidize and basic ferric salts will precipitate (see reactions 
 VI and VII). 
 
 24. The iron must be oxidized (see reaction I) before precipi- 
 tation as the ammonia does not completely precipitate ferrous 
 salts and, even if it did, such a precipitate, t owing to its tendency 
 to oxidize, would be of indefinite composition. 
 
 25. The brown coloration that appears when nitric acid is 
 added is due to the combination of NO with the ferrous sulfate 
 in the solution (see reactions I and II). Upon heating, this com- 
 pound is destroyed and the nitric oxid escapes. 
 
 * "Chemistry of the Metals," Experiment No. 157. 
 t "Chemistry of the Metals," Experiment No. 155. 
 t "Chemistry of the Metals," Experiments Nos. 158 and 160.
 
 GRAVIMETRIC ANALYSIS 55 
 
 Test for complete oxidation by adding a drop or two more of 
 nitric add which, if no ferrous iron remains, will produce 
 no further brown coloration (see reaction II). 
 
 Allow the solution to cool. 
 
 While stirring, add a slight excess of am- Precipitation of 
 monia 26 * 27 (test by the odor). ferric tydroxid 
 
 Heat to incipient boiling with constant stirring. 28 
 
 Allow the precipitate* to settle. 
 
 With hot water, wash several times by decantation through the 
 filter into a 500 c.c. beaker. 
 
 Transfer all of the precipitate to the filter paper Filtration of the 
 and wash with hot water 29 * 30 until a few hydrorid 
 drops of the filtrate no longer give a test washing the 
 for HC1 with AgN0 3 solution.! hydroxid 
 
 EXPLANATORY FACTS 
 
 26. Unless all the iron is precipitated as quickly as possible 
 throughout the solution, SO4 is lost, as basic ferrous sulfate, by 
 being "dragged down" in neutral zones. 
 
 27. The first action upon the addition of ammonia is the neu- 
 tralization of the free acid in the solution, which results in the 
 formation of ammonium nitrate and ammonium chlorid. 
 
 28. In distinction from chromium and aluminium hydroxid, 
 ferric hydroxid is practically insoluble in an excess of ammonia. 
 
 29. Ferric hydroxid may be changed to ferric chlorid if heated 
 with any ammonium chlorid that has been left by insufficient 
 washing. As ferric chlorid is somewhat volatile this would re- 
 sult in a loss of iron (see reaction X). 
 
 30. In order to avoid the solvent action of ammonia upon the 
 glass, filtration must be begun at once after the precipitate has 
 settled. Once begun, the filtration and washing must be com- 
 pleted without delay. 
 
 * "Chemistry of the Metals," Experiment No. 167. 
 f "Chemistry of the Metals," Experiment No. 49.
 
 56 QUANTITATIVE ANALYSIS 
 
 Dry the precipitate in the oven and ignite to a constant 
 weight. 31 * 32 There should not be a greater 
 
 7 \. ., ., ,. .. Drying, igniting and 
 
 variation than three-tenths of a milligram, weighing the pre- 
 Make the final ignition in a covered crucible ci P itate 
 
 over a blast lamp. 
 Report the per cent, of iron. 
 
 EXPLANATORY FACTS 
 
 31. Proper ignition of the precipitate (see reaction V) changes 
 it to Fe2Os. Under reducing conditions, however, reaction VIII 
 may take place and form FesCX or even metallic iron. If sufficient 
 air is admitted to the crucible during ignition, both of these prod- 
 ucts will change to Fe2Os (see reaction IX). 
 
 Reaction V is not completed without the use of the blast 
 lamp. 
 
 32. Fe^Os is hygroscopic: to avoid the absorption of water, it 
 should be weighed as quickly as possible.
 
 GRAVIMETRIC ANALYSIS 57 
 
 DETERMINATION OF THE ACID RADICAL SO 4 
 
 IN AN 
 
 UNKNOWN, SOLUBLE, FERROUS SALT SIMILAR TO 
 FERROUS SULFATE 
 
 SO 4 is: 
 
 (a) precipitated in the presence of hydrochloric acid by 
 barium chlorid, BaCk, as barium sulfate, BaSO 4 ; 
 
 (6) weighed as barium sulfate, BaSO 4 ; 
 (c) calculated as per cent, of S0 4 . , 
 
 REACTION 
 I. (NH 4 ) 2 S0 4 + BaCl 2 = BaS0 4 + 2 NH 4 C1. 
 
 ADDITIONAL REACTIONS POSSIBLE IN THE PROCESS 
 
 II. BaSO 4 + 2 C = BaS + 2 C0 2 . 
 
 III. BaS + 2O 2 = BaS0 4 . 
 
 IV. BaS + H 2 S0 4 = BaS0 4 + H 2 S.
 
 58 QUANTITATIVE ANALYSIS 
 
 DETERMINATION OF THE ACID RADICAL SO 4 
 
 PROCEDURE 
 
 Add hydrochloric acid in slight excess to the filtrate from ferric 
 hydroxid. 33 
 
 On a water bath, evaporate 34 this solution to dryness in a six- 
 inch evaporating 36 dish (see "Evaporation of Liquids," page 
 24). Cover with a watch glass which should rest, not upon 
 the rim of the dish, but upon a glass triangle made of bent 
 stirring rod. This allows steam to escape, Evaporation of 
 catches the spatters and prevents dust from the filtrate 
 falling in. 
 
 EXPLANATORY FACTS 
 
 33. It was necessary to precipitate the iron before the de- 
 termination of sulfur, as (1) the iron tends to contaminate the 
 sulfate and (2) barium sulfate is slightly soluble in ferric 
 chlorid. 
 
 34. During evaporation, both the nitric and the hydrochloric 
 acids are decomposed and volatilized. Should any nitric acid re- 
 main the barium salt of this acid would form and contaminate the 
 precipitate and the final per cent, would be too high. Nitrates of 
 the alkalies and iron are also particularly liable to be dragged 
 down with barium sulfate. 
 
 35. Evaporation is hastened by increasing the top surface of the 
 heated liquid. Broad, shallow dishes, then, are more suited to 
 evaporations than those that are high and narrow. 
 
 Rapid evaporation may be obtained by blowing a gentle cur- 
 rent of warm, dry air onto the surface of the liquid.
 
 GRAVIMETRIC ANALYSIS 59 
 
 Dissolve the residue in 100 c.c. of water and, if necessary, filter 
 the solution. This evaporation is to remove the nitric 
 acid which is here in the form of ammonium nitrate 36 
 and which, in the previous process, was used to oxidize 
 the iron (see reaction I under " The Determination of 
 Iron"). 
 
 Transfer quantitatively to a beaker and add 5 c.c. of dilute 
 hydrochloric 37 acid. 
 
 Heat the covered solution to boiling 38 and, precipitation of the 
 while stirring, add slowly, 39 drop by drop, barium suifate 
 
 EXPLANATORY FACTS 
 
 36. Barium suifate possesses the quality of dragging down with 
 it compounds, even those that are ordinarily soluble. These are 
 not easily removed by washing and, therefore, lead to inaccurate 
 results. 
 
 37. (a) As hydrochloric acid, even when it is dilute, dissolves 
 some barium suifate, only the smallest excess is added. The 
 presence of an excess of BaCk lessens this solubility; a large 
 excess, however, should be avoided as there is danger, especially 
 if the reagent is added quickly, of some of it being precipitated 
 with the barium suifate. 
 
 (6) When sulfuric acid is precipitated by barium chlorid, some 
 of the chlorid is often "dragged down" by the barium suifate. 
 As barium suifate is somewhat soluble, these two sources of error 
 under favorable conditions almost counteract each other. 
 
 38. Barium suifate formed in hot acid solution is in the best 
 condition to be retained by the filter paper. If the solution and 
 the barium chlorid were cold, there would be formed a finely 
 divided precipitate which would have to stand hours before it 
 could be filtered. 
 
 39. If the reagent is added quickly, barium chlorid as well as 
 barium suifate will be precipitated.
 
 60 QUANTITATIVE ANALYSIS 
 
 not exceeding 5 c.c. per minute, a moderate excess of boiling 
 barium chlorid* solution. 40 
 
 After the precipitate has settled, add a few more drops of barium 
 chlorid. Keep the liquid nearly at the boiling point and 
 stir occasionally during one-half hour or more. 
 
 Test for complete precipitation by again adding a few drops of 
 the barium chlorid. 
 
 Pour the supernatant liquid through a special Filtration of the 
 filter, 41 disturbing the precipitate as little sulfate 
 as possible. 
 
 Wash the precipitate twice by decantation with hot water acidi- 
 fied with hydrochloric acid. Then wash washing the 
 with hot water alone and transfer the pre- sulfate 
 cipitate to the filter. 
 
 Wash till the filtrate gives with silver nitrate Testing the gitrate 
 no reaction for chlorids. 42 The filtrate for complete 
 must be clear. washing 
 
 EXPLANATORY FACTS 
 
 40. A soluble barium salt, like barium chlorid, or a soluble 
 sulfate, makes the barium sulfate less soluble. For this reason, 
 it is desirable to have an excess of barium chlorid, but as barium 
 chlorid is carried down with barium sulfate, a large excess should 
 be avoided. 
 
 41. Some of the barium sulfate may run through an ordinary 
 filter. 
 
 42. The absence of chlorids proves that the washing is com- 
 plete. 
 
 * "Chemistry of the Metals," Experiment No. 232.
 
 GRAVIMETRIC ANALYSIS 61 
 
 Dry in the oven, 43 ignite 44 and weigh. Before the second igni- 
 tion add one drop of concentrated sulfuric Drying, ignition 
 acid. Be sure that a constant weight is ad weighing 
 reached. 
 
 Make the final ignition, with the cover on, over the blast lamp. 
 
 EXPLANATORY FACTS 
 
 43. With proper precautions this precipitate can be ignited 
 without putting it into the drying oven (see under "Ignition to a 
 Stable Compound, " page 25, also pages 39 and 40). 
 
 44. Ignite slowly to properly burn the filter paper. Barium 
 sulfate at a high temperature may be reduced by the carbon of 
 the filter paper to barium sulfid. Although sufficient air will 
 usually change the sulfid back to sulfate, the change is sure to 
 take place if sulfuric acid is added.
 
 62 QUANTITATIVE ANALYSIS 
 
 DETERMINATION OF CHLORIN* 
 
 IN 
 AN UNKNOWN, SOLUBLE CHLORID 
 
 (Corresponding to the general formula MCI or MC1 2 ) 
 
 Chlorin is: 
 
 (a) precipitated by silver nitrate, AgNOs, as silver chlorid, 
 
 AgCl,f a type of precipitate which must be removed 
 
 from the filter paper before ignition; 
 (6) weighed as silver chlorid; 
 (c) calculated as per cent, chlorin. 
 
 REACTIONS 
 
 I. MCI + AgN0 3 = AgCl + MN0 3 or 
 II. : MC1 2 + 2 AgN0 3 = 2 AgCl + M(N0 3 ) 2 . 
 
 * Reversed, except in certain special cases, this process may be used for the 
 determination of silver in alloys, etc. 
 
 t Unless it fuses, AgCl is unchanged by ignition, but if it is in contact with the 
 filter-paper when it is ignited, it is reduced by the carbon of the filter paper to 
 netallic silver. Therefore the bulk of the AgCl is removed from the paper, which 
 is burned separately.
 
 GRAVIMETRIC ANALYSIS 63 
 
 DETERMINATION OF CHLORIN 
 
 All silver precipitates and filtrates containing silver salts are 
 to be put into a side-shelf bottle marked " Silver Residues." 
 
 PROCEDURE 45 
 
 Weigh into two 350 c.c. beakers two portions of 
 
 the chlorid, 0.3 of a gram each. charge 
 
 Dissolve in 100 c.c. of cold distilled water. 46 Dissolving the 
 
 Add 3 c.c. of dilute nitric 47 add (sp. gr. 1.2). substance 
 
 EXPLANATORY FACTS 
 
 45. In this determination avoid exposure to bright light.. It 
 changes the silver chlorid from white to violet, which shows a de- 
 composition to a lower chlorid with a loss of chlorin. 
 
 Although later, when the hydrochloric and nitric acids are 
 added, any chlorin that has been lost is replaced (see explanatory 
 fact 52), it is as well to avoid the necessity of correcting previous 
 error. 
 
 46. Silver chlorid is almost insoluble in cold water, but more 
 soluble in hot water. 
 
 47. Nitric acid (1) decreases the solubility of silver chlorid, 
 (2) keeps in solution any other compounds that might be carried 
 down with the silver chlorid and (3) overcomes the tendency 
 which silver chlorid has in cold water of changing to a colloidal 
 state, a condition in which the precipitate will pass through the 
 filter. 
 
 The amount of nitric acid is limited to this amount as silver 
 chlorid is somewhat soluble in concentrated nitric acid.
 
 64 QUANTITATIVE ANALYSIS 
 
 Add silver nitrate solution, drop by drop, with constant stirring, 
 until there is no further precipitation.* Precipitation of 
 There should be a slight excess of the silver ** chlorid 
 nitrate. 48 
 
 Heat nearly to the boiling point 49 and stir constantly until the 
 precipitate has coagulated and the liquid is clear. 
 
 Place the solution in a dark place to settle. 
 
 Use filter papers 9 cm. in diameter. 
 
 Pour the liquid through the filter without Filtration of the 
 greatly disturbing the precipitate. silver chlorid 
 
 Catch the filtrate in a 500 c.c. beaker. 
 
 Wash the precipitate in the beaker three times with cold water 
 slightly acidified with nitric acid 50 , decant- washing the 
 ing the liquid through the filter. chlorid 
 
 EXPLANATORY FACTS 
 
 48. An excess of silver nitrate, as in the case of nitric acid, de- 
 creases the solubility of silver chlorid and aids in the coagulation 
 of the precipitate. 
 
 If the precipitate is not flocculent there is probably not a suffi- 
 cient excess of silver nitrate. 
 
 49. Do not heat to boiling before the silver nitrate is added in 
 excess, as some of the unprecipitated chlorin might be liberated 
 from the original salt (KC1, NaCl, etc.) by the action of the hot 
 nitric acid. 
 
 The heat is necessary to make all the precipitate floc- 
 culent. 
 
 50. Nitric acid prevents the coagulated precipitate from return- 
 ing to a colloidal state. 
 
 * "Chemistry of the Metals," Experiment No. 49.
 
 GRAVIMETRIC ANALYSIS 65 
 
 Transfer the precipitate to the filter and continue the washing 
 with cold water acidified with nitric acid Testing ^^ ffltrate 
 until a drop of hydrochloric acid in 3 c.c. of for complete wash- 
 the wash water shows no turbidity. 51 Be "* 
 sure to wash the filter paper clean above the pre- 
 cipitate. 
 
 Wash twice with cold water or a mixture of alcohol and water, 
 half and half, to remove the nitric acid. Test for the 
 absence of nitric acid with litmus paper. Save the filtrate 
 for silver recovery. 
 
 Dry the precipitate in the oven at 100 C. This precipitate 
 cannot be ignited with the filter paper, as Drying the pre- 
 the carbon from the paper will reduce silver P itate 
 chlorid to metallic silver. 
 
 Place a perfectly clean three-inch watch glass upon a circular 
 piece of glazed paper about six inches in diameter. 
 
 Separate the silver chlorid from the filter paper in the following 
 manner: Remove the filter from the funnel. Gently 
 loosen the precipitate adhering to the sides Special precautions 
 of the paper by pressing the funnel-shaped 
 paper with the thumb and fingers. With 
 great care, empty the contents of the filter paper upon the 
 watch glass. Invert the filter paper over the watch glass 
 and carefully rub the sides together. Avoid rubbing hard 
 enough to detach threads of the paper. Cover the pre- 
 cipitate with an inverted six-inch watch glass. 
 
 EXPLANATORY FACT 
 
 51. Mixed with the AgCI are nitrates of the alkali metals that 
 were in combination in the original salt and nitrate of silver. 
 The absence of the latter in the HC1 test indicates that the other 
 soluble nitrates are also washed away.
 
 66 QUANTITATIVE ANALYSIS 
 
 After removing the precipitate, press the filter paper into the 
 shape of a quarter circle, fold in halves lengthwise, fold once 
 again in the same way. Roll the top edge and secure it by 
 fastening around it loosely a platinum wire. If there is any 
 silver chlorid on the edge of the paper the heat will reduce 
 it to metallic silver, which will alloy with the platinum. This 
 will break the wire and spoil the determination as well. 
 
 Hold the folded filter paper by the wire over a weighed porcelain 
 crucible, which should be on a piece of glazed paper. Burn 
 and let the ash fall into the crucible. 
 
 Place the crucible on its side on a clay triangle. As silver 
 chlorid volatilizes at rather a low temperature, apply the 
 Bunsen flame only on that part of the cru- ignition of the 
 cible upon which there rest particles of chlorid 
 carbonaceous matter. When these have whitened, remove 
 the lamp and cool the crucible. 
 
 Add to the ash two drops of concentrated nitric acid to dissolve 
 the metallic silver* and then two drops Treatment of any 
 of concentrated hydrochloric acid to convert reduced silver 
 it to the chlorid. 
 
 Evaporate to dry ness on the water bath. 
 
 Transfer the main part of the precipitate which is on the watch 
 glass into the crucible. Hold the watch glass over the 
 glazed paper and brush off into the crucible the remaining 
 particles with a small brush or trimmed feather. Finally 
 brush into the crucible any particles that may be on the 
 glazed paper. 
 
 Add to the precipitate two drops of concentrated nitric acid and 
 two drops of concentrated hydrochloric 52 acid. 
 
 EXPLANATORY FACT 
 
 52. It is at this point that the silver chlorid which has been 
 reduced to metallic silver by sunlight is dissolved and changed 
 back to the chlorid 
 
 * "Chemistry of the Metals," Experiment No. 46.
 
 GRAVIMETRIC ANALYSIS 67 
 
 Evaporate to dryness on the water bath. 
 
 Heat with great care until the silver chlorid barely begins to fuse 
 at its edges. 53 If it is heated too strongly the deter- 
 mination will be ruined. weighing the 
 
 Cool and weigh. cMorid 
 
 Heat, cool and weigh until a constant weight is obtained. 
 
 EXPLANATORY FACT 
 
 53. Silver chlorid slightly decomposes and volatilizes at its 
 temperature of fusion, 460 C.
 
 QUANTITATIVE ANALYSIS 
 
 DETERMINATION OF CALCIUM AND MAGNESIUM 
 
 IN 
 MIXED CARBONATES 54 
 
 1. The soluble constituents are dissolved from the mineral, 
 the solution is evaporated to dryness and the residue dehydrated. 
 This leaves insoluble siliceous matter. 
 
 2. Iron and aluminium are precipitated by ammonium hydroxid, 
 NH 4 OH, as ferric hydroxid, Fe(OH) 3 , and aluminium hydroxid, 
 A1(OH) 3 . 
 
 3. Manganese, if present, is precipitated by ammonium hy- 
 droxid, after oxidation with bromin, as an oxid of varying com- 
 position. 
 
 1, 2 and 3 are not weighed. They are simply to be removed 
 and rejected before the calcium and magnesium are precipitated. 
 
 4. Calcium is: 
 
 (a) precipitated by freshly prepared ammonium oxalate solu- 
 tion (NHOzCaO^ as calcium oxalate, CaC 2 O 4 ; 
 (6) changed by ignition to calcium oxid and weighed as such; 
 (c) calculated as per cent, calcium oxid. 
 
 5. Magnesium is: 
 
 (a) precipitated by microcosmic salt, NaNEUHPO^ as crys- 
 talline magnesium ammonium phosphate, MgNH4P04; 
 
 (6) changed by ignition to magnesium pyrophosphate, MgzPzOy, 
 and weighed as such; 
 
 (c) calculated as per cent, of magnesium oxid. 
 
 EXPLANATORY FACT 
 
 54. Such a mixture is found in dolomite (magnesium lime- 
 stone). This is one of the common minerals whose composition 
 is CaCOs . MgCOs in varying proportions. It may also contain 
 manganese, aluminium, iron, silica, etc.
 
 GRAVIMETRIC ANALYSIS 
 
 REACTIONS 
 Calcium and Magnesium 
 
 I. CaCO 3 + 2 HC1 = CaCl 2 + H 2 O + CO 2 . 
 
 II. MgCO 3 + 2 HC1 = MgCl 2 + H 2 O + CO 2 . 
 
 III. H 4 Si0 4 + A = 2 H 2 + Si0 2 . 
 
 IV. CaCl 2 + (NH 4 ) 2 C 2 4 = CaC2O 4 + 2 NI^Cl. 
 V. CaC 2 4 + 2 HC1 = CaCl 2 + H 2 C 2 O 4 . 
 
 VI. CaCl 2 + H 2 C 2 4 + 2 NH 4 OH = CaC 2 O 4 + 2 NH 4 C1 
 
 + 2H 2 0. 
 
 VII. CaC 2 4 + A = CaO + CO 2 + CO. 
 VIII. MgCl 2 + NaNH 4 HP0 4 = MgHP0 4 + NaCl + NH 4 CL 
 IX. MgHP0 4 + NH 3 = MgNH4P0 4 . 
 X. 2 MgNH 4 P0 4 + A = Mg2P 2 7 + 2 NH 3 + H 2 0.
 
 70 QUANTITATIVE ANALYSIS 
 
 DOLOMITE 
 
 PROCEDURE 
 
 Weigh into 350 c.c. beakers two portions of the weighing the 
 finely ground mineral of 1.5 grams each. char e 
 
 REMOVAL OF THE SILICEOUS MATTER 55 
 
 Treat in covered beakers with hydrochloric acid* Dissolving the 
 (1.12 sp. gr.) until action ceases (see re- substance 
 actions I and II). . 
 
 Transfer quantitatively into evaporating dishes and evaporate 
 to dryness on a water bath. Dehydration of the 
 
 Heat for two hours at 130 C. (see reaction III). sUicic acid 
 
 Cool and add to the residue a few drops of concentrated hydro- 
 chloric acid. 
 
 EXPLANATORY FACT 
 
 55. The siliceous residue, composed of quartz, clay, etc., is 
 largely insoluble in the dilute acid. Some soluble silicic acid 
 may, however, pass into solution. It must be heated at 130 C. 
 to change it to insoluble silica, SiC>2, which can be filtered off. 
 
 The mineral could be dissolved directly in an evaporating dish 
 but it is somewhat easier to judge of cessation of solution if the 
 action takes place in glass. 
 
 * " Chemistry of the Metals," Experiment No. 240.
 
 GRAVIMETRIC ANALYSIS 71 
 
 Warm cautiously and then add 20 c.c. of hydrochloric acid (1.12 
 
 sp. gr.) and 20 c.c. of water. 
 While warm, filter into a beaker. 
 Wash the residue on the filter paper with hot Removal of the 
 
 water till it is free from hydrochloric acid, s^ceous residue 
 
 when it may be rejected. 
 
 REMOVAL OF ALUMINIUM M AND IRON w (AND MANGANESE) 
 
 If a qualitative test has shown the presence of manganese, 58 it is 
 precipitated at this point by adding bromin water to the 
 filtrate from the silica till a permanent yel- Remo7al of ^^ 
 low color remains. Then proceed with the aluminium and 
 addition of NH 4 C1 and NH 4 OH as in the man * anese 
 following paragraph. 
 
 If manganese is absent add a few drops of nitric acid to the fil- 
 trate from the silica and boil to be sure that the iron is all 
 oxidized. Add the least possible excess of ammonium 
 hydroxid. Gently boil the solution till it is but faintly 
 ammoniacal. 
 
 Quickly 59 filter the precipitated iron and aluminium hydroxid 
 (and perhaps manganese) and wash three or four times 
 with hot water. 
 
 Mark the filtrate and washings "A." 
 
 EXPLANATORY FACTS 
 
 56 and 57. See notes under aluminium and iron determina- 
 tions. 
 
 58. It is necessary to add bromin to oxidize the manganese, 
 which, with ammonia, forms a hydrated dioxid. This hydrated 
 dioxid of manganese is thus removed with the iron and alu- 
 mina. 
 
 59. Filter quickly to avoid action of ammonia upon the glass 
 and also to avoid the absorption of carbon dioxid.
 
 72 QUANTITATIVE ANALYSIS 
 
 Dissolve * the precipitate of iron, aluminium solution of the iron, 
 
 (and manganese) on the filter paper with 
 
 hot, dilute hydrochloric add, receiving this tates 
 
 solution in a separate beaker. 
 
 Thoroughly wash the acid solution out of the paper. 
 Test washings with litmus paper. 
 If manganese is not present, add a slight excess Re eci itatLon of 
 
 of ammonia water to reprecipitate the the iron, aluminium 
 
 iron and aluminium from this acid solu- andman sanese 
 
 tion. 
 If manganese is present, again add a few drops of bromin 
 
 water before adding the ammonia. 
 Boil till only faintly ammoniacal. 
 
 Filter and wash free from chlorids. Reject the precipitate. 
 Mark the filtrate and washings "B." 
 
 EXPLANATORY FACT 
 
 60. This re-solution and reprecipitation is necessary to com- 
 pletely separate the small quantity of calcium which may have 
 precipitated as carbonate, due to absorption of atmospheric C02 
 by the alkaline solution.
 
 GRAVIMETRIC ANALYSIS 73 
 
 DETERMINATION OF THE CALCIUM 
 
 This element is now contained in the filtrate and washings "A" 
 from the original iron and aluminium precipitate and in the filtrate 
 and washings "B" from the second precipitation of iron and 
 aluminium (and possibly of manganese). 
 
 Combine the filtrates "A" and "B" and heat to boiling. 
 
 Evaporate to 250 c.c. if it exceeds this volume. 
 
 Make alkaline with ammonium hydroxid. 
 
 To the boiling ammoniacal liquid, add slowly, with stirring, a 
 moderate excess of warm, freshly pre- precipitation of the 
 pared 61 ammonium oxalate 62 solution * (see "fc" <*aiate 
 reaction IV). 
 
 Heat to boiling for a few minutes and let the precipitate settle 
 for half an hour or more. 
 
 Decant the liquid, but do not remove the precipitate to the 
 filter, as it is to be redissolved. 
 
 Wash the precipitate by decantation three or four times with 
 hot water till free from ammonium chlorid, washing by de- 
 testing the wash water with silver nitrate 
 acidified with nitric acid. 
 
 EXPLANATORY FACTS 
 
 61. Ammonium oxalate decomposes slowly and ammonium car- 
 bonate is one product of this decomposition. 
 
 62. Calcium oxalate is somewhat dissolved by magnesium chlorid 
 solution; therefore, enough ammonium oxalate should be added 
 to convert to oxalate the magnesium as well as the calcium. 
 
 * "Chemistry of the Metals," Experiment No. 242.
 
 74 QUANTITATIVE ANALYSIS 
 
 Test the filtrate for complete precipitation with a few drops of 
 ammonium oxalate and let it stand. This filtrate, when 
 combined with the filtrate obtained from Treatment of the 
 the reprecipitated calcium oxalate (see ^h^precf^tation 
 below), if perfectly clear, is ready for the of the magnesium 
 magnesium determination. 
 
 Without delay, slightly acidify the filtrate, to prevent the solvent 
 action of the alkali upon the glass. 
 
 If the filtrate is more than 150 c.c. in volume, evaporate it on 
 the water bath. The precipitate, if the original sample 
 contained much magnesium, will contain some magnesium 
 oxalate with the calcium oxalate. 
 
 Purify 63 the calcium oxalate as follows: redissolve the pre- 
 cipitate on the filter and in the beaker by pm^^^ of ^ 
 pouring warm, dilute hydrochloric acid first calcium ox- 
 (see reaction V) four or five times through alate precipltate 
 the filter into the beaker containing the precipitate. After 
 the calcium oxalate is all dissolved, wash the filter with 
 ammonium hydroxid. Dilute the solution to about 250 c.c. 
 Heat and make it slightly alkaline with ammonium hydroxid 
 (see reaction VI). Add 5 c.c. of the ammonium oxalate 
 solution 64 and let it stand for at least half an hour. 
 
 EXPLANATORY FACTS 
 
 63. Although magnesium oxalate is relatively soluble, espe- 
 cially in the presence of ammonia salts, yet as calcium oxalate may 
 drag down some magnesium oxalate, a re-solution and reprecipi- 
 tation is necessary. On second precipitation, there is relatively 
 so little magnesium present that none of it is contained in the 
 calcium oxalate precipitate. 
 
 64. This ammonium oxalate is added to insure the presence of 
 an excess of the reagent, the best condition for the precipitation 
 of the calcium.
 
 GRAVIMETRIC ANALYSIS 75 
 
 Filter through the same filter paper as used Filtration ^ wash . 
 
 before. ing of the reprecipi- 
 
 Wash the precipitate with hot water. teted calcium oxalate 
 
 Test the filtrate for chlorids and, when the precipitate is free, 
 slightly acidify the filtrate and add it to the first filtrate 
 containing the bulk of the magnesium oxalate. The com- 
 bined filtrates should not exceed 200 to 300 c.c. 
 
 Dry the precipitated calcium oxalate in the oven. 
 
 Ignite in a platinum 65 crucible. Heat strongly Drying, ignition 
 for about ten minutes. and weighing 
 
 Finish with a blast lamp for ten minutes 66 (see reaction VII). 
 
 Repeat until a constant weight is obtained. 
 
 EXPLANATORY FACTS 
 
 65. A higher temperature than that which is needed by many 
 precipitates is required for the complete conversion of the calcium 
 oxalate to calcium oxid. Although a porcelain crucible may be 
 used, in this case one of platinum is better. 
 
 66. Weigh quickly, as calcium oxid absorbs moisture from the 
 air.
 
 76 QUANTITATIVE ANALYSIS 
 
 DETERMINATION OF MAGNESIUM 
 METHOD OF WOLCOTT GIBBS 
 
 Concentrate 67 the filtrates containing the magnesium (and 
 ammonium) salts to about 200 c.c. and bring to a boil. 
 
 Add to the almost boiling solution several drops of methyl 
 orange and, to make neutral, add ammonia, drop by drop, 
 till the solution just becomes yellow. Keep hot. 
 
 Add a normal solution of microcosmic salt, ^60^^^,, of ti, e 
 NaNH 4 PO4,* till no further precipitation magnesium ammo- 
 takes place 68 (see reaction VIII). ** phosphate 
 
 While stirring, add a volume of ten per cent, ammonia equal to 
 one-third that of the hot solution 69 (see reaction EX). 
 
 EXPLANATORY FACTS 
 
 67. If during concentration any magnesium oxalate settles out, 
 decant the liquid into another beaker, dissolve the salt in dilute 
 hydrochloric acid and combine. 
 
 68. Almost ninety per cent, of the magnesium present is at once 
 thrown down as amorphous magnesium hydrogen phosphate, 
 MgHPO 4 . 
 
 69. The addition of ammonia and the stirring transform the 
 magnesium hydrogen phosphate into crystalline magnesium ammo- 
 nium phosphate, MgNHiPCU. Simultaneously the remaining 
 magnesium is almost completely thrown down. The complete 
 precipitation is effected upon standing two or three hours. 
 
 * "Chemistry of the Metals," Experiment No. 260.
 
 GRAVIMETRIC ANALYSIS 77 
 
 Let stand two or three hours to insure complete precipita- 
 tion. 
 
 Decant the liquid through the filter. 
 
 Wash the precipitate three times by decantation Fatenng and wash- 
 with a wash water made by mixing one a^n^riu^hos^ 1 
 part of ammonia (sp. gr. 0.96) and five parts phate 
 of water. 
 
 Transfer to the filter and wash till the filtrate gives with silver 
 nitrate no reaction for chlorids. 
 
 Dry in the hot closet. 
 
 Transfer the bulk of the dried precipitate to a weighed porcelain 
 crucible. 
 
 Burn the filter paper in a platinum wire spiral and add the ash 
 to the precipitate in the crucible. 
 
 Heat the covered crucible very gently until the ammonia is 
 driven off and the precipitate is white. Igni tion, cooling 
 Then heat 70 more strongly (see reaction X) . and 
 
 Cool in a desiccator. 
 
 Ignite to a constant weight. Use the blast lamp if necessary. 
 
 EXPLANATORY FACT 
 
 70. During this ignition, great care should be used to avoid 
 the reduction of the pyrophosphate.
 
 78 QUANTITATIVE ANALYSIS 
 
 DETERMINATION OF SILICA, SiO 2 , 
 
 IN 
 GLASS OR OTHER INSOLUBLE SILICATES 
 
 The silicate is: 
 
 (a) converted by fusion with an alkali carbonate into a form 
 decomposable by hydrochloric acid. The metals are 
 converted to carbonates while the silicic acid forms sili- 
 cates of potassium and sodium. 
 
 (6) dissolved in hydrochloric acid with formation of chlorids 
 and free silicic acid. 
 
 (c) silicic acid is dehydrated to silica, SiO 2 . 
 
 (d) filtered, ignited, weighed and calculated as silicon dioxid, 
 
 Si0 2 . 
 
 REACTIONS 
 
 I. 2M 2 "Si0 4 + 4NaKC0 3 = 4M 
 
 or 
 II. 2 M"Si0 3 + 2 NaKC0 3 = 2 M"C0 3 + Na^SiOa + K 2 Si0 3 . 
 
 III. M"CO 3 + 2 HC1 = MC1 2 + H 2 + C0 2 . 
 
 IV. Na4Si0 4 + 4 HC1 = 4 NaCl 
 
 or 
 
 V. Na2Si0 3 + 2HCl = 2NaCl 
 VI. EUSiO* + A = 2 H 2 O + SiO 2 
 
 or 
 
 VII. H 2 SiO 3 + A = H 2 O + SiO 2 . 
 VIII. SiO 2 + 4 HF = SiF 4 + 2 H 2 O.
 
 GRAVIMETRIC ANALYSIS 79 
 
 DETERMINATION OF SILICA 
 
 PROCEDURE 
 
 Grind the mineral in an agate mortar to an impalpable powder. 
 The correctness of the determination de- Grinding and 
 pends upon this being perfectly done. weighing the charge 
 
 Weigh into platinum crucibles two portions of the substance, 
 0.2 of a gram each. 
 
 Add 2 grams of sodium potassium carbonate, NaKCOs 1 to each 
 and mix. To avoid loss by frothing, 72 the Fusion with an 
 crucible should never be filled more than alkali ""^nate 
 one-half full. The carbonate can be added in small portions 
 during the fusion. 
 
 Heat gently until the frothing ceases. When melted, heat for 
 fifteen minutes or longer over a blast lamp until tranquil 
 fusion results. 
 
 EXPLANATORY FACTS 
 
 71. By this fusion all the insoluble substances are transformed 
 into such compounds as carbonates, silicates of the alkalies, etc., 
 which are all decomposed by hydrochloric acid. The final solu- 
 tion, then, is composed of chlorids of those metals present and 
 silicic acid. According to the amount present, the silicic acid is 
 wholly or in part in solution. 
 
 72. The frothing is caused by the evolution of the carbon 
 dioxid gas.
 
 80 QUANTITATIVE ANALYSIS 
 
 After the lamp has been removed and when the crucible is just 
 below redness, cool suddenly 73 by placing it on an inverted 
 porcelain mortar, or stone desk- top. 
 
 When thoroughly cooled, invert the crucible on a piece of glazed 
 paper and remove the fused cake. 
 
 Place the crucible with its adhering pieces of the fused mass and 
 its cover hi a beaker. 
 
 Add 100 c.c. of water, cover, warm and from time to time 
 add a little dilute hydrochloric acid till Preparation of the 
 all of the adhering substance is dis- solution 
 solved. 
 
 Remove the crucible and its cover with a stirring rod and care- 
 fully wash them both off into the beaker. 
 
 Put the fused cake from the glazed paper into the beaker and 
 dissolve it with about 50 c.c. of hydrochloric acid (sp. gr. 
 1.12). Keep the beaker closely covered to avoid loss from 
 effervescence. 74 
 
 Transfer the acid solution to an evaporating dish or casserole 
 and evaporate to dryness on a steam bath. 
 
 Heat in a hot Closet at 130 C. for tWO hours Dehydration of the 
 
 (see reactions VI & VII). silicic acid 
 
 Cool and add a few drops of concentrated hydrochloric 
 
 acid. 
 
 Warm cautiously. To the warm solution add 20 c.c. of hydro- 
 chloric acid (sp. gr. 1.12) and then 20 C.C. Filtration and wash- 
 
 of water. Again warm gently. *"* of the sUica 
 
 While warm, filter into a beaker. 
 
 EXPLANATORY FACTS 
 
 73. This loosens the mass from the side of the crucible. 
 
 74. Silicic acid, which is slightly soluble in water and in acids, 
 is a white gelatinous mass. It appears yellow as it is suspended 
 in a yellow solution.
 
 GRAVIMETRIC ANALYSIS 81 
 
 Wash the residue on the filter paper till free from hydrochloric 
 
 acid. Ignition and weigh- 
 
 Dry, ignite in a platinum crucible and weigh. 75 " 
 
 EXPLANATORY FACT 
 
 75. After a constant weight has been obtained, a test of the 
 purity of the silica consists in volatilizing the silica with hydro- 
 fluoric acid, HF (see reaction VIII). The silicon tetrafluorid 
 formed volatilizes, while compounds of any admixed metals, if 
 present, remain in the crucible. Deduction of the weight of 
 this nonvolatile residue from the constant weight of silica ob- 
 tained, gives the weight of the pure silica.
 
 SECTION II 
 
 ELECTROLYTIC ANALYSIS 
 
 83
 
 ELECTROLYTIC ANALYSIS. 
 
 lonization 
 
 WHEN most compounds are dissolved, their molecules are dis- 
 sociated, breaking down into ions, and the process is called ioniza- 
 tion or dissociation. 
 
 Ions are electrically charged and in this respect differ from atoms 
 or molecules. 
 
 A molecule of common salt, NaCl, is composed of atoms of 
 sodium and chlorin, each of which has its definite characteristics. 
 When these atoms of sodium and chlorin become electrically 
 charged and have become ions, their characteristics have changed. 
 Metallic sodium decomposes water and forms sodium hydroxid, 
 but if this same sodium becomes ionized, it exists in water with- 
 out chemical change. When this ion loses its electric charge, 
 it immediately decomposes the water, forms sodium hydroxid and 
 liberates hydrogen. 
 
 That these ions are electrically charged can be demonstrated. 
 Two conducting plates acting as electrodes, the poles of an open 
 electric circuit, one positive and the other negative, are immersed 
 in a dilute solution of common salt. Immediately the sodium is 
 attracted to the negative pole. The negative pole loses some of its 
 negative charge and, it is supposed, neutralizes the positive charge 
 of the sodium ion, which assumes the atomic state and shows 
 the characteristics of metallic sodium by decomposing water to 
 form sodium hydroxid. The chlorin is attracted to the positive 
 
 85
 
 86 QUANTITATIVE ANALYSIS 
 
 pole which loses some of its charge of positive electricity, presum- 
 ably neutralizing the negative charge of the chlorin ion. The 
 chlorin escapes at the positive pole and has all the characteristics 
 of chlorin in its ordinary state. 
 
 A solution of a dissociated substance is called an electrolyte. The 
 greater the dilution the more complete the dissociation. 
 
 Electrolysis 
 
 The process of decomposition of a chemical compound in solu- 
 tion by the electric current is called electrolysis. The compound 
 is decomposed into two parts, each of which may be simple, like 
 copper, Cu, or complex, like SCX 
 
 Hydrogen or metallic ions formed in solution by dissociation 
 and charged with plus electricity are attracted to the negative 
 pole or cathode and are therefore called cations. 
 
 Nonmetallic ions formed in solution by dissociation and charged 
 with negative electricity are attracted to the positive pole or 
 anode and are therefore called anions. 
 
 The current passes through the liquid between the two metallic 
 surfaces, electrodes. These may be plates, spirals, cones, etc., 
 according to the method to be employed. They may be fixed or 
 arranged to rotate. The current enters by the positive pole, the 
 anode, and leaves by the negative pole of the circuit, the cathode. 
 The anions separate at the anode and the cations at the cathode. 
 
 In the following determination the metals silver and copper 
 are cations and are therefore separated at and deposited on 
 the cathode. The acid radical of the nitrates separates at the 
 anode. 
 
 Current density is the proportion of the strength of the current 
 to the electrode surface and is usually expressed by amperage per 
 100 sq. cm. In the potassium cyanid solution used here (see p. 88) 
 the approximate current density used for silver is 2.5 volts and 
 0.06-0.1 ampere per 100 sq. cm. and that of copper is 5 volts and 
 1 ampere. 
 
 Silver is thus first deposited and then the copper is determined 
 in the remaining solution by using a higher current density. The
 
 ELECTROLYTIC ANALYSIS 87 
 
 metals are deposited on weighed electrodes and the per cent, deter- 
 mined by the observed increase in weight. 
 
 Such processes save time, are cleaner and lend themselves to 
 easier manipulation than is the case with ordinary gravimetric 
 methods. The use of electrolysis for analysis is rapidly increas- 
 ing. The following is but one of the many now established for 
 the separation and determination of metals alone or hi the presence 
 of others.
 
 88 QUANTITATIVE ANALYSIS 
 
 THE ELECTROLYTIC SEPARATION* 
 
 OF 
 COPPER AND SILVER f 
 
 A Type of Electro-Analysis 
 
 (a) The alloy is dissolved in nitric acid, forming nitrates of silver 
 
 and copper. 
 (6) The excess of nitric acid is removed by evaporation. 
 
 (c) An excess of potassium cyanid is added. 
 
 (d) With proper strength of current, the silver is deposited on a 
 
 weighed platinum electrode. 
 
 (e) With the proper strength of current, the copper is deposited 
 
 on a similar electrode. 
 
 REACTIONS 
 
 I. Ag + 2 HNO 3 = AgNO 3 + H 2 O + NO 2 . 
 
 II. 3 Cu + 8 HN0 3 = 3 Cu(N0 3 ) 2 + 4 H 2 + 2 NO. 
 
 III. AgN0 3 + 2 KCN = KAg(CN) 2 + KNO 3 . 
 
 IV. 2 Cu(NO 3 ) 2 + 4 KCN = 2 Cu(CN) 2 + 4 KN0 3 . 
 V. 2 Cu(CN) 2 = (CN) 2 + 2 CuCN. 
 
 VI. 2 CuCN + 6 KCN = 2 (CuCN.3 KCN). 
 
 * This particular method has been selected because of its simplicity. The 
 directions, which are for an alloy high in copper, may by slight modifications be 
 used for the common alloy, coinage silver (see Fact 76) . 
 
 t Smith and Frankel, J. A. C. S., 1890, p. 104; Smith and Spencer, J. A. C. S., 
 1894, p. 420; Smith and Fulweiler, J. A. C. S., 1901, p. 682; Electro-Analysis, Edgar 
 F. Smith, 1907.
 
 ELECTROLYTIC ANALYSIS 
 
 DETERMINATION OF SILVER AND COPPER 
 PROCEDURE * 
 
 Weigh one portion of about 0.5 of a gram of sil- 
 ver-copper alloy 76 into a 250 c.c. casserole. 
 Read Fact 77 and then dissolve the alloy in the 
 
 Dissolving the alloy 
 
 least possible amount of nitric add (1.4 
 
 sp. gr.). 
 
 Evaporate to dryness on the water bath. 
 While this is on the water bath, clean with sapolio and then 
 
 chromic acid the platinum electrode that preparation of a 
 
 is to be used as the cathode. cathode 
 
 Wash it with distilled water until it is thoroughly rinsed. 
 Hold it in the pincers and pass it through a flame till it is red 
 
 hot. 
 Put it into a desiccator to cool. 
 
 EXPLANATORY FACTS 
 
 76. If coinage silver ninety parts of silver to ten of copper 
 is used for this determination, use less KCN than in the above 
 directions, allow more time for depositing the silver and less for 
 depositing the copper. A quarter of a ten-cent piece weighs about 
 0.7 of a gram. 
 
 77. All excess of nitric acid must be removed in the next step 
 by evaporation to dryness. KCN must not be added to an acid 
 solution. It would evolve volatile HCN, which is a poison. 
 
 * This process is given through the courtesy of Edgar F. Smith, Professor of 
 Chemistry at the University of Pennsylvania. His experiments were made with an 
 alloy of approximately ten parts of silver to ninety parts of copper.
 
 90 QUANTITATIVE ANALYSIS 
 
 When cool, weigh and note the weight. 
 
 When the above solution is evaporated to dryness, dissolve the 
 residue in hot water. 
 
 Transfer the solution quantitatively to a 100 c.c. volumetric 
 measuring flask.* 
 
 Wash down the inside of the neck and add distilled water till 
 the meniscus (see page 99) is exactly at the 100 c.c. line on 
 the neck. Dry the inside walls of the neck above the line 
 with a piece of filter paper rolled around a stirring rod. 
 
 Pour the solution back and forth into a perfectly dry beaker till 
 it is thoroughly mixed. When not in use keep this meas- 
 uring flask closely stoppered to prevent evaporation. 
 
 Measure with a 25 c.c. volumetric measuring flask or pipet 78 
 
 exactly 25 c.c. of the solution. This is an Measuring an 
 . aliquot part, one-quarter of the solution. "<* pa rt 
 
 Pour this aliquot part into a small dry beaker holding about 
 200 c.c. With distilled water wash out several times the 
 25 c.c. flask to be sure that the solution is quantitatively 
 transferred. 
 
 Dilute to about 125 c.c. 
 
 Read Fact 79 and then, following precautions, add about 2 
 grams 80 of the potassium cyanid, KCN.f 
 
 EXPLANATORY FACTS 
 
 78. Aliquot parts, or definite fractions of the whole volume of 
 a uniform solution, should be measured only in dry measuring 
 dishes or in those which have been washed out with several small 
 portions of the solutions to be measured. 
 
 79. Potassium cyanid is a violent poison! The student must 
 handle it with the greatest care! He must wash his hands care- 
 fully after using it and at no time during this experiment should 
 he drink from laboratory dishes. 
 
 80. The amount of KCN added varies according to the relative 
 per cent, of the copper and silver. Use approximately 2 grams of 
 KCN for each 0.1 of a gram of copper. 
 
 * Read the paragraph on "Measuring Flasks," page 99. 
 
 t "Chemistry of the Metals," Experiments Nos. 49 and 104.
 
 ELECTROLYTIC ANALYSIS 91 
 
 DETERMINATION OF SILVER 
 
 With the aid of the instructor, attach the weighed cathode to the 
 negative pole of the circuit and the anode to the positive 
 pole. 
 
 Arrange the two electrodes about one centimeter apart in 
 the solution. Do not let them touch the Electrolytic 
 bottom of the beaker. deposition 
 
 Use a current density of approximately 2.5 volts and 0.06 to 0.1 
 of an ampere for 100 sq. cm. of cathode surface. 81 
 
 Heat the solution to a temperature 82 of about 65 C. 
 
 Test with a thermometer but, to avoid loss when it is taken out, 
 wash it off into the solution. 
 
 Switch on the electric current for the deposition of the silver and 
 allow from two to three hours. 
 
 At the end of two hours one drop of the solution Test for complete 
 may be tested for silver. deposition of silver 
 
 When there is no silver left in the solution and the deposition 
 is therefore shown to be completed, have at hand bottles of 
 alcohol and ether, a wash bottle and a piece of filter paper 
 laid on a five-inch watch glass. The following work should 
 be done expeditiously. 
 
 EXPLANATORY FACTS 
 
 81. Unless connections have been used in previous work and 
 the terminals marked, it will be necessary to determine before- 
 hand by experiment which is the negative pole. This can be done 
 by the use of an ammeter upon which the poles are marked or by 
 passing a current through a dilute copper sulfate solution in which 
 there are two unweighed platinum electrodes. The copper is de- 
 posited on the negative electrode. 
 
 82. At a temperature of 65 C., 0.2 to 0.3 of a gram of silver 
 may be precipitated in four hours. If the solution is cold, it will 
 probably take ten hours for 0.2 of a gram to precipitate.
 
 92 QUANTITATIVE ANALYSIS 
 
 Lift the cathode from the solution. 
 
 Wash it thoroughly with a stream of water Preparation of the 
 
 from the wash bottle, catching the wash- 
 
 ings in the beaker. 83 
 Pour alcohol M completely over each side of the electrode. 
 Do the same with ether. 
 
 Place the cathode on the filter paper on the watch glass. 
 Put the watch glass in an air bath that is not hotter than 100 C., 
 
 for a few moments only, until dry. Lest the cathode be for- 
 gotten, do nothing else until it is dry. 
 Place in a desiccator, cool and weigh. Note the weight. 
 After the final weight has been made, in a beaker dissolve the 
 
 silver from the cathode with hot, dilute nitric add. 
 Put this solution in the "silver residue" bottle. Wash the 
 
 cathode, polish it with sapolio, clean it thoroughly, dry, 
 
 ignite and weigh. 
 Leave it in the desiccator ready for the next deposition. 
 
 DETERMINATION OF COPPER 
 
 The silver has been removed but the solution still contains the 
 copper which did not deposit at so low a current density. The 
 potassium cyanid which was added at the start is still present. 
 The best working volume under these conditions has been found 
 to be 150 c.c. 
 
 This solution is probably, because of previous washings, about 
 150 c.c. If not, evaporate it to this volume. 
 
 EXPLANATORY FACTS 
 
 83. The solution that clings to the cathode contains some of 
 the copper which is to be quantitatively determined. 
 
 84. Do not pour alcohol and ether near a flame. Allow 
 "washings" to fall into a clean, dry beaker to be saved in 
 "residue bottles."
 
 ELECTROLYTIC ANALYSIS 93 
 
 PROCEDURE 
 
 Add 10 c.c. of ammonium hydroxid^ NH 4 OH (0.96 sp. gr.). 
 
 Arrange the electrodes as before. 
 
 Use a current density of approximately 5 volts and 1 ampere 
 
 for 100 sq. cm. 
 
 Keep the temperature of the solution at 65 C. 
 At 65 C., about 0.2 of a gram of copper will Deposition of the 
 
 be deposited in an hour. c pp er 
 
 Two hours therefore should be allowed. At the end of this time, 
 
 add a little distilled water to the solution to raise its level. 
 If no new copper appears on the fresh surface of the platinum, 
 
 the deposition may be considered complete. 
 Lift the cathode from the solution and wash quickly and thor- 
 oughly with distilled water. 
 Wash with alcohol and with ether as before, Preparation of the 
 
 save washings in the "residue bottles." 
 Place the cathode on a filter paper on a watch 
 
 glass and put in an air bath not hotter than 100 C. till dry, 
 
 but no longer. 
 
 Cool in a desiccator and weigh. 
 After the weight has been made, dissolve the copper from the 
 
 cathode with dilute nitric acid. 
 Wash the cathode and as previously described prepare it for the 
 
 check analysis. 
 
 EXPLANATORY FACT 
 
 85. In alkaline cyanid solution, there is a tendency for the 
 platinum of the anode to be deposited with the copper on the 
 cathode. If, however, the cyanid is not largely in excess, and if 
 the current is interrupted as quickly as possible after the copper 
 is deposited, this error is reduced to a minimum. It has been 
 determined that in the presence of a definite amount of ammonium 
 hydroxid there is absolutely no loss sustained by the anode in 
 cyanid electrolyte and that the precipitation is much acceler- 
 ated ("Electro- Analysis," Smith, page 71).
 
 94 QUANTITATIVE ANALYSIS 
 
 Duplicate Analysis 
 
 Use another aliquot part of 25 c.c. of the original solution and 
 make a check analysis of both the silver and copper.
 
 SECTION III 
 
 VOLUMETRIC ANALYSIS 
 
 95
 
 VOLUMETRIC ANALYSIS 
 
 Comparison of Volumetric and Gravimetric Methods 
 
 IN Gravimetric Analysis the element or radical to be determined is 
 either isolated or combined in an insoluble compound and weighed. 
 This process of isolation or combination often requires a series of 
 careful and prolonged operations. In Volumetric Analysis (1) the 
 element or radical to be determined is not necessarily isolated but 
 is often treated in the presence of the other constituents. To make 
 this possible, the exact qualitative content should be known and 
 all reactions that are likely to occur in the course of the analysis 
 should be understood. (2) In the oftentimes greater simplicity of 
 the processes involved, in the fewer weighings, and in the usual 
 absence of much filtering and washing, the chance of error is less 
 than in Gravimetric Analysis and (3) the saving of time, especially 
 in a case of routine work which requires the analysis of many 
 samples a day, is very great. 
 
 Volumetric Analysis is the quantitative determination of an 
 element or radical in a substance, a determination, as its name 
 indicates, made by adding a volume of a selected solution sufficient 
 to cause definite, complete reaction. 
 
 97
 
 98 QUANTITATIVE ANALYSIS 
 
 Measuring Instruments 
 
 For the accurate measurement of liquids there are certain 
 graduated glass vessels, the pipet, measuring cylinder, measuring 
 flask and buret. 
 
 For the best results, it is most important that the measuring 
 instruments be graduated accurately and that they agree among 
 themselves. 
 
 In a longer course of Volumetric Analysis it is customary 
 to have the students calibrate* to verify the capacity of these 
 instruments. In this short course, if possible, it would be well 
 for the department to have the instruments calibrated and 
 to issue calibration cards showing the variation of the instru- 
 ments. If this is not possible the errors, which are often slight, 
 may be ignored and a wider latitude allowed in the results 
 obtained. 
 
 Pipets are used to measure exactly small amounts of solutions. 
 They are either graduated to deliver a specified quantity, such as 
 10 c.c., 50 c.c., etc., or are graduated in fifths or tenths of a cubic 
 centimeter to deliver any desired fractional part of the whole 
 quantity. The pointed end of the pipet is dipped into the 
 solution, the mouth is applied to the other end and the liquid 
 sucked into the pipet up to the mark. The forefinger is placed 
 over the top end to keep the solution from running out. The 
 pressure of the finger regulates the flow from the pipet. In case 
 of a " one-quantity " pipet, to insure complete delivery, the pipet 
 should be inclined against the side of the dish and the last drop fi ^ 
 blown out. Pipets are graduated to deliver their contents; the 
 mark is therefore high enough to include the liquid that adheres to 
 
 * For methods of calibrating pipets, flasks, cylinders and burets, see Button's 
 "Volumetric Analysis," pages 18-20.
 
 ' VOLUMETRIC ANALYSIS 99 
 
 the inside walls; in other words, it delivers into another receptacle 
 the exact amount marked, but holds a trifle more. The point of 
 a pipet should be sufficiently fine so that the liquid will not be 
 delivered too quickly. 
 
 Measuring flasks, stoppered glass vessels with narrow necks, are 
 graduated either to deliver or to contain or both, in which latter 
 case the upper mark is that of delivery. Each measuring flask and 
 pipet should have etched upon it its capacity, the temperature 
 at which the graduation was made and the line that marks the 
 limit of definite content. A specially constructed flask has along 
 the length of the inside wall of its neck a broad blue line on 
 a background of white enamel. This facilitates the reading by 
 the reflection of the blue on the "meniscus" the curved line 
 of the surface of the liquid which makes the blue line narrow 
 into a point. 
 
 Measuring cylinders, glass cylinders of varying sizes, are gradu- 
 ated to deliver and are used for mixing and for making compara- 
 tively rough measurements. 
 
 Burets, graduated glass tubes of large bore, with cocks at the 
 lower end for controlled delivery, are graduated in fifths, tenths 
 or twentieths of a cubic centimeter and hold twenty-five, fifty or 
 one hundred cubic centimeters. The two common forms of buret 
 are the Geissler, or Fresenius, type with glass stopcock and the 
 Mohr type with a rubber tip closed with a metal pinchcock or a 
 glass ball acting as a valve. Burets are supported upon stands. 
 One convenient model is the Chaddock, in which the burets are 
 held by easily manipulated wire clips which prevent slipping and 
 hold the buret firmly vertical. The white porcelain base serves 
 as an excellent background against which end points are well 
 determined.
 
 100 QUANTITATIVE ANALYSIS 
 
 Reading the Instruments 
 
 The surface of liquids in narrow vessels is, because of capillary 
 attraction, concave and, in the case of mercury, convex. This 
 makes it necessary to select some point on the curved line to 
 coincide with the graduation mark in the instrument. In the 
 case of all light-colored liquids, it has been found advisable to 
 select the lowest point of the concave line, the bottom point 
 of the "meniscus"; with dark or opaque liquids, the highest point 
 on the extreme upper level. 
 
 Before reading any graduated instrument, its exact vertical posi- 
 tion must be assured. 
 
 In reading a buret, the eye should be on a level with the selected 
 point of the meniscus and its position in relation to the graduated 
 lines on the buret noted. 
 
 If the student is not provided with a buret made with a longi- 
 tudinal blue line on a white, enameled background, he may, with 
 advantage, hold a piece of dark glazed paper at the back of the 
 buret about one-eighth of an inch below the surface of the liquid. 
 This will make the lower part of the meniscus appear as a well- 
 defined black line against the white. 
 
 A buret reading should not be taken until all liquid which may 
 cling to the walls of the buret has had time to flow into the main 
 bulk of the liquid. Three minutes is the usual time allowed for 
 the liquid to collect. A uniform rate of delivering the liquid should 
 be adopted. After a rapid run it takes more time for the liquid to 
 collect than after a slow run.
 
 VOLUMETRIC ANALYSIS 101 
 
 General Directions 
 
 The perfect cleanliness of the volumetric measuring apparatus 
 is essential. Grease, which makes the liquid gather in drops on the 
 walls, may be removed with a dilute solution of sodium hydroxid, 
 NaOH; or acidified potassium dichromate, K 2 Cr 2 O7, or chromic 
 acid, CrO 3 . 
 
 Any volumetric instrument even if new and dry should be rinsed 
 out with three successive small portions of the solution with which 
 it is to be filled. It is absolutely necessary that all standard solu- 
 tions should be kept at their known established strength, that they 
 should not be diluted with any drops of water which may be 
 adhering to the walls of the measuring vessels and that they should 
 not be contaminated with any foreign matter. 
 
 In Volumetric Analysis to insure accurate results the conditions 
 should be kept as uniform as possible, conditions of intensity 
 of light, temperature, time of waiting before taking readings, 
 reading of tenths and end points. To practise the reading of 
 tenths, the buret may be filled with water and, as it is allowed to 
 escape drop by drop, the surface of the water, as the level is 
 lowered, may be watched and its exact position noted in reference 
 to the graduation lines. In this way, accurate reading of the 
 tenths is easily mastered.
 
 102 QUANTITATIVE ANALYSIS 
 
 Standard Solutions 
 
 A solution whose exact content per cubic centimeter has been 
 determined is a standard solution and is said to have been stand- 
 ardized. 
 
 The process of adding a definite quantity of a standardized 
 liquid to a solution to estimate its value or to a solution of a sub- 
 stance to be analyzed is called titration. 
 
 An acid solution, for instance, is standardized and alkali titrated 
 with it to estimate the value of the alkali in terms of the acid and 
 vice versa. A solution of a salt is standardized to be used for the 
 oxidation, reduction or precipitation of the solution to be analyzed. 
 'A solution of known composition and standard strength is used 
 to cause a complete, definite reaction with a solution of the sub- 
 stance to be analyzed. For example, a solution of ammonium 
 sulfo-cyanid whose exact strength is known is added to a solution 
 of silver nitrate to be analyzed. These react as follows: 
 
 AgN0 3 + NH4SCN = AgSCN + NH^Oa. 
 
 When the silver in the silver nitrate is entirely changed to sulfo- 
 cyanid, another drop of the ammonium sulfo-cyanid will form no 
 further precipitate (see under " End Point" 2, b). The strength 
 of the ammonium sulfo-cyanid is known and also the exact amount 
 in cubic centimeters that it took to precipitate the silver. From 
 this data and the relation of the molecular weights the amount of 
 silver present in the silver nitrate can be calculated.
 
 VOLUMETRIC ANALYSIS 103 
 
 End Point 
 
 The exact point at which such reactions are complete is called 
 the end point. The end point is shown: 
 
 1. By the persistence of the color of the standard solution used. 
 This shows the completion of chemical action. Thus: A solution 
 of ferrous sulfate is titrated with a standardized solution of potas- 
 sium permanganate in the presence of sulfuric acid, 
 
 2 KMn0 4 + 10 FeSO 4 + 8 H 2 S0 4 
 
 = 2 MnSO 4 + 5 Fe 2 (S0 4 ) 3 + K 2 SO 4 + 8 H 2 0. 
 
 The color of the standard solution, KMnO 4 , is pink. Just as 
 long as any of the ferrous sulfate is left, the potassium perman- 
 ganate continues to decompose and to lose its pink color. When 
 the reaction is completed, the permanganate is no longer decom- 
 posed and its pink color persists. 
 
 2. By the formation of, or change in, the color of a substance, 
 called an indicator, originally added for this purpose to the solution 
 to be analyzed. Thus: 
 
 a. With an organic indicator, such as methyl orange, in the 
 presence of alkalies its red color changes to yellow or, again, 
 colorless phenolphthalein in the presence of alkalies turns bright 
 red. 
 
 6. With an inorganic indicator, such as ferric chlorid in the 
 following illustration, after the main reaction is completed, the 
 soluble, red Fe(SCN) 3 , is formed. 
 
 NH 4 N0 3 
 3NH 4 C1 
 
 3. By the formation of a precipitate. Thus: A standardized 
 solution of silver nitrate is added to a solution of potassium 
 
 AgN0 3 + 
 Substance to 
 be analyzed 
 
 NH 4 SCN = 
 Standard 
 solution 
 
 AgSCN 
 
 White 
 precipitate 
 
 FeCl 3 + 
 Soluble, color not 
 noticed when dilute 
 
 3NH4SCN = 
 
 First drop 
 in excess 
 
 Fe(SCN) 3 
 Soluble, 
 red
 
 104 QUANTITATIVE ANALYSIS 
 
 chlorid to be analyzed, in which there is an indicator, potassium 
 chromate. 
 
 KC1 + AgN0 3 = AgCl + KN0 3 . 
 
 When all of the potassium chlorid has been used to form white 
 silver chlorid, the next drop of the reagent, silver nitrate, reacts 
 with the potassium dichromate to form silver chromate which is 
 red. 
 
 K 2 CrO 4 + 2 AgNO 3 = Ag2CrO 4 + 2 KNO 3 . 
 Indicator Red 
 
 4. By the failure to produce color when a drop of the solution 
 being analyzed is added to an indicator in a separate container. 
 Thus: A standardized solution of potassium dichromate is added 
 to a solution of ferrous chlorid to be analyzed in the presence of 
 hydrochloric acid, 
 
 K 2 O 2 O 7 + 6 FeCl 2 + 14 HC1 
 
 = 6 FeCl 3 + 2 KC1 + 2 CrCl 3 + 7 H 2 O. 
 
 The indicator, potassium ferricyanid, is in a separate dish. If, 
 before the reaction is completed, a stirring rod is dipped into the 
 above solution and then into the indicator, there is formed a blue 
 precipitate, according to the equation, 
 
 3 FeCl 2 + 2 K3Fe(CN) 6 = Fe 3 (Fe(CN) 6 ) 2 + 6 KC1. 
 Indicator Blue 
 
 When the ferrous chlorid is all oxidized to ferric chlorid and a drop 
 of the solution is added to the indicator, there will be no color, 
 according to the equation, 
 
 FeCl 3 + K3Fe(CN) 6 = FeFe(CN) 6 + 3 KCL 
 Indicator Colorless
 
 VOLUMETRIC ANALYSIS 105 
 
 Indicators 
 
 Indicators as illustrated above are used to show, by color changes 
 or by a precipitation, a condition of acidity, alkalinity, neutrality 
 or, in general, the completion of reaction. They may be (1) dye- 
 stuffs; (2) the coloring matters of plants, which are generally weak 
 acids; salts of weak acids or, less often, weak bases; or (3) in- 
 organic compounds which form a coloration or a colored precipi- 
 tate at the end of a reaction. 
 
 An indicator must take no part in the reaction going on but as 
 the reagent is added must itself remain inert till the main reaction 
 is completed. After the completion of the reaction, the next drop 
 of the liquid acts on the indicator in the solution and gives ocular 
 evidence that the end point has been reached. There is no one 
 indicator that can be universally used. That which answers for 
 one analysis may be useless for another. Its value depends upon 
 the sensitivity of its action and upon the sharpness and intensity 
 of the color it affords. 
 
 Indicators have been divided by R. T. Thomson* into three 
 classes : (1) Those capable of forming stable salts, as methyl orange. 
 These are most sensitive to alkalies. (2) Those forming unstable 
 salts which hydrolyze hi water, as phenolphthalein. These are 
 most sensitive to acids. (3) Those midway between the two, as 
 litmus. These are fairly sensitive to both alkalies and acids. 
 
 The theories of the action of indicators are by no means final. 
 According to Ostwald, an indicator, for at least acids and bases, 
 must possess a color when undissociated different from that which 
 it has when ionized. f That is, the color changes are ascribed to 
 the dissociation and caused by the addition of a substance to 
 the indicator. It is, therefore, the color reaction caused by the 
 hydrogen or hydroxyl ions of dissociated acids or bases which 
 makes some dyes of service as indicators. 
 
 * J. S. C. I., volume 6, 1887, page 195. 
 
 t Ostwald's "Lehrbuch der Allgemeinen Chemie."
 
 106 QUANTITATIVE ANALYSIS 
 
 Strong acids and strong bases, since they ionize readily, are not 
 useful as indicators. Weak acids and weak bases are more or less 
 undissociated in solution and are ionized only after conversion to 
 a neutral salt. 
 
 This will be made clear by the following examples : 
 
 (a) Phenolphthalein, belonging to class 2, a weakly acid 
 indicator, is undissociated and colorless in acid solution. Its 
 alkali salt is, however, at once dissociated and the red color of 
 the ion at once shows the completion of the neutralization of 
 the solution. 
 
 (6) Methyl Orange, belonging to class 1, a moderately 
 strong acid indicator, is undissociated and of a pinkish red color 
 in acid solution. When an acid solution containing the indicator 
 methyl orange is titrated with a solution of an alkali, the first 
 drop of alkali after the end point has been reached forms a salt 
 with the methyl orange. The salts of methyl orange are readily 
 dissociated, whereupon the red of the nonionized indicator changes 
 to yellow, the color of the ion.* 
 
 The following are but a few of the indicators in general use: 
 litmus, methyl orange, phenolphthalein and lacmoid. 
 
 Litmus 
 
 With acids red. 
 
 With alkalies blue. 
 
 This is a violet-blue, organic pigment sensitive to both acids 
 and alkalies. It cannot be used with bicarbonates and carbon- 
 ates, as the liberated carbonic anhydrid dissolves and causes the 
 red color to persist even if the liquid is alkaline. It can, however, 
 be used if the solution is boiling, as this gas is then constantly 
 evolved. 
 
 Methyl Orange 
 
 With acids pinkish red. 
 
 With alkalies yellow. ' 
 
 This is the sodium or ammonium salt of a specific organic acid, 
 synthetically prepared. It is an ochre yellow powder which when 
 
 * For further study of this subject, the student is referred to such textbooks as: 
 Jones's "Theory of Electrolytic Dissociation" and Cohn's "Indicators and Test 
 Papers," from which some of the above statements are taken.
 
 VOLUMETRIC ANALYSIS 107 
 
 dissolved in water forms a yellow solution. Methyl Orange is 
 particularly sensitive to alkalies. An excess of this indicator 
 should be avoided, as the color changes are then not so sharp. 
 The yellow color is not affected by alkalies or by carbonates of 
 the alkalies, but is changed to a pinkish red by acids, becoming 
 yellowish red on approaching neutralization. 
 
 Carbonic, boric, silicic, arsenious and some organic acids, in- 
 cluding some of the fatty acids, do not cause methyl orange to 
 change to red. 
 
 Phenolphthalein 
 
 With acids colorless. 
 
 With alkalies red. 
 
 This is an organic compound synthetically prepared. It is a 
 cream-white, crystalline powder. Phenolphthalein has the prop- 
 perties of a very weak acid and is extremely sensitive. Even 
 carbonic acid causes a change. Titrations, therefore, in the 
 presence of carbonates, can be done only in boiling solution. One 
 part of alkali in 100,000 parts of water will give a distinct color. 
 It cannot be used in the presence of ammonium salts. 
 
 Lacmoid 
 
 With acids red. 
 
 With alkalies violet blue. 
 
 This is another organic compound synthetically prepared. It 
 is in the form of blue-black scales. Lacmoid is sensitive to both 
 acids and alkalies. It can be used in the presence of carbonates 
 only in hot solution.
 
 108 QUANTITATIVE ANALYSIS 
 
 Normal Solutions 
 
 /N\ 
 A normal solution ( yj is one that contains in one liter as many 
 
 grams of the active substance as its molecular weight divided 
 either by its replaceable hydrogen atoms or the equivalent of such 
 hydrogen atoms. 
 
 (A) Reagents with replaceable hydrogen atoms, such as 
 HC1, H 2 S0 4 . 
 
 1. The molecular weight of HC1 = 36.45. This expressed 
 
 in grams is 36.45 grams. HC1 has one replaceable 
 hydrogen atom; therefore, 36.45 -* 1 = 36.45, the 
 weight required. 
 
 A normal solution of HC1 contains in one liter 36.45 
 grams of HC1. 
 
 2. The molecular weight of H 2 SO 4 = 98.07. This ex- 
 
 pressed in grams is 98.07 grams. H 2 S04 has two 
 replaceable hydrogen atoms; therefore, 98.07 -4- 2 
 = 49.03, the weight required. 
 
 A normal solution of H 2 S04 contains in one liter 49.03 
 grams of H 2 SO 4 . 
 
 (B) Reagents containing no replaceable hydrogen atoms, such 
 as NaOH, K 2 Cr 2 O 7 and SnCl 2 . 
 
 3. The molecular weight of NaOH is 40.058. This ex- 
 
 pressed in grams is 40.058 grams. Na is monovalent 
 and therefore equivalent to one atom of replaceable 
 hydrogen. 
 
 A normal solution of NaOH, therefore, contains in one 
 liter 40.058 grams of NaOH.
 
 VOLUMETRIC ANALYSIS 109 
 
 The equivalent of the replaceable hydrogen atoms differs accord- 
 ing to the reaction that is to take place. Potassium dichromate, 
 for example, can be used either as a precipitating or as an oxidiz- 
 ing agent. 
 
 4. As a precipitating agent, potassium dichromate reacts 
 as follows: 
 
 2 Ba(C 2 H 3 O 2 )2 + K 2 Cr 2 O 7 + H 2 O 
 
 = 2 BaCr0 4 + 2 KC 2 H 3 2 + 2 HC 2 H 3 2 . 
 
 In this reaction, for every molecule of the reagent K 2 Cr 2 07, two 
 molecules of BaCrO 4 are precipitated, which require two atoms 
 of Ba in the two molecules of Ba(C 2 H 3 O 2 ) 2 . Each atom of Ba 
 is equivalent to two of H, therefore the two atoms of Ba used in 
 this precipitation are equivalent to four atoms of hydrogen. 
 
 In a normal solution of potassium dichromate used as a pre- 
 cipitant, then, its equivalent in replaceable hydrogen atoms is four. 
 
 The molecular weight of K 2 Cr 2 O 7 = 294.5. 
 This expressed in grams is 294.5 grams. 
 294.5 + 4 = 73.62. 
 
 A normal solution of potassium dichromate used as a precipitant 
 contains in one liter 73.62 grams. 
 
 5. As an oxidizing agent, potassium dichromate reacts 
 as follows:,, ^ 
 
 * 6 FeCl 2 + K 2 Cr ? 7 + 14 HC1 = 
 
 6 FeCl 3 + 2 CrCl 3 + 2 KC1 + 7 H 2 0. 
 
 In this process of oxidation, K 2 Cr 2 O 7 acts as if it split up into 
 K 2 0, Cr 2 3 and O 3 . Each molecule of K 2 Cr 2 07 frees three atoms 
 of O for oxidizing purposes. In the above reaction, for three 
 atoms of O liberated in a molecule of the reagent K 2 Cr 2 O 7 , 
 there are six atoms of chlorin liberated to combine with the 
 ferrous chlorid to form ferric chlorid. Six atoms of Cl are 
 equivalent to six atoms of H. 
 
 * "Chemistry of the Metals," Experiment No. 200.
 
 110 QUANTITATIVE ANALYSIS 
 
 In a normal solution of potassium dichromate used as an oxidiz- 
 ing agent, its equivalent in replaceable hydrogen atoms is six. 
 
 The molecular weight of K 2 Cr 2 7 = 294.5. 
 This expressed in grams = 294.5 grams. 
 294.5 grams -J- 6 = 49.08 grams. 
 
 A normal solution of potassium dichromate used as an oxidizing 
 agent contains in one liter 49.08 grams, one-sixth of its molecular 
 weight in grams. 
 
 6. As a reducing agent stannous chlorid reacts as follows : 
 SnCl 2 + 2 FeClg = 2 FeCl 2 + Sn<Cl 4 . 
 
 In this reaction, every molecule of the reagent, SnCl 2 , reduces 
 two molecules of the ferric chlorid (2 FeCls) to two molecules of 
 ferrous chlorid (2 FeCl 2 ). Each molecule of the SnCl 2 , then, 
 removes two atoms of chlorin which are the equivalent of two 
 atoms of hydrogen. This may also be shown by the reaction 
 
 <* V In 
 
 H 2 + 2 FeCl 3 = 2 FeCl 2 + 2 HC1. 
 
 In a normal solution of stannous chlorid used as a reducing agent, 
 its equivalent in hydrogen atoms is two. 
 
 The molecular weight of SnCl 2 = 189.90. 
 
 This number expressed in grams = 189.90 grams. 
 
 189.90 -5- 2 = 94.95 grams. 
 
 A normal solution of the reducing agent stannous chlorid contains 
 in one liter 94.95 grams of SnCl 2 , one-half of its molecular weight in 
 grams. 
 
 A solution of one-half the strength of a normal solution is called 
 a seminormal solution ( -^-j 
 
 A solution of one tenth of the strength of a normal solution is 
 
 (N\ 
 To)' etc '
 
 VOLUMETRIC ANALYSIS 111 
 
 Permanency of Standard Solutions 
 
 Solutions of the nature of those just described do not remain 
 of the same strength for an indefinite period of time. Evapora- 
 tion and chemical changes, including those resulting from the action 
 of light, and action upon the glass of the bottle all contribute to 
 render a standardization accurate for a comparatively limited 
 time only. Thus, silver nitrate is reduced in the light and silver 
 is deposited, weakening the solution; potassium permanganate 
 deposits oxids of manganese, and sodium hydroxid reacts with 
 the glass of the bottle. Even at normal temperature, a solution 
 of any substance evaporates and the solvent condenses on the 
 sides of the bottle or, if imperfectly corked, it escapes into the air. 
 It is therefore necessary to keep the bottle carefully stoppered, to 
 keep it in a cool dark place and to shake it thoroughly in order 
 to wash down its inner wall before using. It is also advisable not 
 to make up too large a quantity of solution of a substance that 
 acts upon the glass. Any solution about whose exact strength 
 there is any doubt should be restandardized.
 
 112 QUANTITATIVE ANALYSIS 
 
 Acidimetry and Alkalimetry 
 
 The processes of Acidimetry and Alkalimetry are those by which 
 the strength of acids and bases are determined. 
 
 STEPS TO BE CONSIDERED IN PREPARING AND STANDARDIZING 
 
 HALF-NORMAL SOLUTIONS OF HYDROCHLORIC ACID AND 
 
 SODIUM HYDROXID 
 
 (1) Preparation of an approximately half -normal solution of 
 hydrochloric acid. 
 
 (2) Preparation of an approximately half-normal solution of 
 sodium hydroxid. 
 
 (3) The titration of the acid against the alkali for the deter- 
 mination of the relative values of the approximately half-normal 
 solutions of hydrochloric acid and sodium hydroxid. 
 
 (4) The use, through factors, of approximately half-normal solu- 
 tions as standard solutions. 
 
 (5) The determination with Iceland spar or pure sodium car- 
 bonate of the absolute value of the approximately half-normal 
 solution of hydrochloric acid and the preparation of an exactly half- 
 normal solution of hydrochloric acid. 
 
 (6) The preparation of an exactly half-normal solution of sodium 
 hydroxid by use of the previously established values. 
 
 (7) The determination with oxalic acid of the absolute value of 
 the approximately half-normal solution of sodium hydroxid and 
 the preparation of an exactly half-normal solution of sodium 
 hydroxid. 
 
 (8) The reestablishment of the relative values of the two solu- 
 tions, which, if correctly diluted, should now be equal, volume for 
 volume.
 
 VOLUMETRIC ANALYSIS 113 
 
 (1) Preparation of an Approximately Half -Normal Solution of 
 Hydrochloric Acid 
 
 Theoretically the simplest way to prepare accurate standard 
 solutions is to dissolve calculated and carefully measured amounts 
 of substances in an exact amount of solvent. As a matter of fact, 
 however, neither the conditions nor the chemicals used in most 
 cases are sufficiently to be relied upon to give perfect results. 
 
 An approximately normal solution can be made and its relative 
 value to an exactly normal solution can be determined or an exactly 
 normal solution can be prepared from the one that is approximately 
 normal. 
 
 CALCULATION OF THE NUMBER OF CUBIC CENTIMETERS OF 
 
 AQUEOUS HYDROCHLORIC ACID REQUIRED TO MAKE A 
 
 LITER OF A HALF-NORMAL SOLUTION 
 
 As a solution of hydrochloric acid gas is to be used, it is necessary 
 to calculate the weight of the hydrochloric acid gas contained in 
 the aqueous hydrochloric acid. 
 
 A normal solution of HC1 should contain 36.458 grams of HC1 
 gas in one liter. 
 
 At 15 C., HC1 (sp. gr. 1.2) contains 39.1% of HC1 by weight. 
 In 100 c.c. of aqueous HC1 (sp. gr. 1.2) there are 46.92 grams of 
 HC1 gas for: 
 
 100 c.c. 
 
 1.2 
 
 120 grams = weight of 100 c.c. of aqueous HCL 
 
 .391 X 120 grams = 46.920 grams. 
 46.92 grams = weight of HC1 gas in 100 c.c. of aqueous HCL
 
 114 QUANTITATIVE ANALYSIS 
 
 To furnish 36.458 grams of HC1 gas, there must be 77.70 c.c. of 
 aqueous hydrochloric acid (sp. gr. 1.2) according to the following 
 proportion: 
 
 . 46.92 : 36.458 :: 100 : x 
 x = 77.70 c.c. 
 
 N 
 In a liter of a normal solution of hydrochloric acid, -y > then, 
 
 there are 77.7 c.c. of aqueous hydrochloric acid (sp. gr. 1.2). 
 
 N 
 In a half-normal solution, -^, there are in every liter one-half of 
 
 77.7 c.c. or 38.85 c.c. of aqueous HC1 (sp. gr. 1.2) measured at 
 15 C. 
 
 PROCEDURE 
 
 In a graduated cylinder measure a volume approximately equal 
 to 38.8 c.c. of aqueous hydrochloric acid (sp. gr. 1.2) and 
 about one-tenth as much in addition. 86 
 
 Add enough distilled water to dilute to one liter and shake 87 for 
 a minute or more. If the cylinder is too full 
 to allow the liquid to be shaken thoroughly, Preparation of the 
 
 u i j.- J standard acid solu- 
 
 transfer to a beaker, stir vigorously and tion 
 return the solution to the bottle. 
 
 N 
 Label the bottle " Approximately --HCl". 
 
 EXPLANATORY FACTS 
 
 86. The extra volume is added to make sure that it is stronger 
 than half-normal. It is easier later to dilute than to add an 
 exact amount of acid. 
 
 87. It is of the utmost importance to get the solution into a 
 homogeneous state.
 
 VOLUMETRIC ANALYSIS 115 
 
 ?) Preparation of an Approximately Half-Normal Solution of 
 Sodium Hydroxid 
 
 PROCEDURE 
 
 Calculate in the notebook the amount of caustic soda, NaOH, 
 necessary to make one liter of a half-normal solution. 
 
 Weigh 89 out on a rough balance in a counterbalanced porcelain 
 dish an amount equal to the calculated weight plus one- 
 tenth as much in addition. 90 
 
 Measure 1000 c.c. of distilled water in a measuring cylinder. 
 
 Dissolve the sodium hydroxid in a part of this Preparation of the 
 distilled water contained in a beaker or standard aikaii 
 porcelain dish. 
 
 Stir until the hydroxid is all dissolved and then cover with a 
 watch glass till it is somewhat cooled. 
 
 Transfer the solution to a bottle, add the rest of the distilled 
 water and shake vigorously. 
 
 Label the bottle, which must have a rubber stopper or a 
 glass stopper light ly covered with vaseline, 
 
 "Approximately NaOH ". 
 
 EXPLANATORY FACTS 
 
 88. Standard acid solutions may be kept for some time with- 
 out deterioration. This is not the case with standard alkali 
 solutions which absorb carbon dioxid from the air and, as has 
 been said, act upon the glass of the bottles in which they are con- 
 tained. It is therefore important to titrate the alkali frequently 
 with a standard acid in order to reestablish its strength. 
 
 89. Weigh quickly and do not leave exposed to the air, as 
 caustic soda is hygroscopic. Cork the stock bottle at once. 
 
 90. Sodium hydroxid, caustic soda, is an excellent alkali for 
 general use; it is a strong base, forms soluble salts with all acids 
 and, being readily soluble (133.3 parts in 100 parts of water), may 
 be made up to a strong solution.
 
 116 QUANTITATIVE ANALYSIS 
 
 (3) The Titration of the Acid against the Alkali 
 
 and 
 
 The Calculation of the Relative Values of the Approximately 
 
 Half-Normal Solutions of Hydrochloric 
 
 Acid and Sodium Hydroxid 
 
 PROCEDURE 
 
 Wash two burets thoroughly with distilled water. When they 
 
 are emptied, no drops should adhere to the inner walls. 
 
 If they do, the surface is not clean and should be treated 
 
 with "chromic acid mixture." 
 Put a label on the top front of each buret, one Labeling the 
 
 marked "HC1" and the other "NaOH". b * ets 
 Fit a cork to each and label each cork, one marked "HC1" the 
 
 other "NaOH". Keep a small, properly labeled watch 
 
 glass upon which to lay each cork. 
 Close the outlet of the "HC1" buret and 
 
 . x . . Filling the burets 
 
 pour in 5 c.c. of the again well-shaken 
 
 IHCI. 
 
 Hold the stoppered buret in a nearly horizontal position and 
 allow the acid to flow over the entire interior and shake. 
 Then remove the cork and let the acid run out through 
 the outlet. 
 
 This should be repeated. 
 
 Treat the "NaOH" buret in the same way. (If it is certain 
 that the burets are absolutely dry, the foregoing may be 
 omitted.) 
 
 Put a small glass funnel into the top of each buret with the 
 stem against the inner wall and fill each buret with its well- 
 shaken solution.
 
 VOLUMETRIC ANALYSIS 117 
 
 Let enough of each liquid run through the tips to insure the 
 
 removal of any air bubbles. 
 If there are any drops of the liquid left on the inner walls of the 
 
 burets above the zero mark, absorb with a filter paper rolled 
 
 around a glass rod. 
 
 Be sure that the burets are perfectly vertical. 
 Run out the liquid in each buret till the bottom of the meniscus 
 
 stands at the zero mark. If a "blue line" buret is used, 
 
 bring the constriction seen on the blue line to the zero mark. 
 If the liquid is below the zero mark, make a careful reading at 
 
 such a point. 
 Record the reading in the notebook. It is well to keep the 
 
 HC1 and NaOH readings in the same relative positions on 
 
 the page as the positions of the burets (see next page). 
 Run about 40 c.c. of the add into a casserole, an Erlenmeyer or 
 
 an ordinary flask, containing about 40 c.c. of distilled water, 
 
 and add two or three drops of methyl 
 
 . .. _, m -xi Titration process 
 
 orange indicator. To mix well, stir with a 
 rod or shake the flask with a rotary motion. 
 
 Include any drop hanging from the tip of the buret by touching 
 it with the rod or with the inside of the neck of the flask 
 and washing it down with water from a wash bottle. 
 
 Run into the container about 5 c.c. less of the sodium hydroxid 
 than that used of the hydrochloric acid and then slowly con- 
 tinue to add the sodium hydroxid solution, drop by drop, till 
 the pinkish red solution turns yellow. Again do not neglect 
 any hanging drops of the solution. Wash down the sides of 
 the dish with distilled water. 
 
 Place the container under the HC1 buret and continue to change 
 from one buret to the other till one drop of the HC1 or one 
 drop of the NaOH changes the color. 
 
 As the pink is the sharper of the two color reactions, finish by 
 adding a drop of HC1. 
 
 After a few minutes' wait for it to drain, note the reading of the 
 HC1 buret.
 
 118 
 
 QUANTITATIVE ANALYSIS 
 
 Continuing this, make six successive readings of these repeated 
 changes and record as follows: 
 
 Readings. 
 HC1 
 level at start, 1.34 
 
 Actual number of 
 c.c. used. 
 
 41.83 
 1.34 
 40.49 
 
 Relative Values. 
 
 Actual number of 
 c.c. used. 
 39.1 
 0.5 
 38.6 
 
 Readings. 
 NaOH 
 
 levelatstart,0.5 
 
 c.c. 
 41.83 
 41.98 
 42.15 
 42.29 
 42.49 
 42.69 
 
 c.c. 
 
 40.49 
 40.64 
 40.81 
 40.95 
 41.15 
 41.35 
 
 .048 
 .048 
 .048 
 .047 
 .047 
 .047 
 
 c.c. 
 
 38.6 
 38.75 
 38.93 
 39.08 
 39.27 
 39.45 
 
 C.C. 
 
 39.1 
 39.25 
 39.43 
 39.58 
 39.77 
 39.95 
 
 
 
 Average 1.0475 
 
 
 
 Therefore 1 c.c. of NaOH solution is equivalent to 1.0475 c.c. 
 of HC1 solution. 
 
 Shake the bottles containing the half-normal solutions, refill the 
 
 burets and repeat the titration. 
 These results should check within 0.2 per cent, of the whole ratio.
 
 VOLUMETRIC ANALYSIS 119 
 
 (4) The Use Through Factors of Approximately Half-Normal 
 Solutions as Standard Solutions. 
 
 Those limited in time need not prepare the exactly half-normal 
 solutions, since the value of, or the degree of normality of, the 
 approximately half-normal solutions may be determined by 
 calculation. 
 
 It is, however, oftentimes desirable to have exact solutions. 
 Thus, as shown in the accompanying sample calculation (see 
 
 page 126), 38.24 c.c. of exactly ^HCl dissolves 0.9567 gram of 
 
 Zi 
 
 CaC0 3 whereas this same weight of CaC0 3 dissolved ha 34.49 c.c. 
 of this particular solution of HC1. 
 
 N 38 24 
 
 The approximately -^ solution of HC1 is therefore ^-p ^ = 1,108 
 
 tunes stronger than semi-normal, the factor of normality for the 
 
 N 
 approximately 77- HCl solution. 
 
 N 
 A given number of cubic centimeters of an exact -~ NaOH 
 
 solution is exactly equivalent to the same number of cubic centi- 
 
 N 
 
 meters of an exact -5- HCl solution. But in establishing the abso- 
 lute value of the HCl solution (see sample calculation p. 125) it 
 
 N 
 was found that 40.0 c.c. approximately -^-NaOH solution neutra- 
 
 N 
 lized 43.65 c.c. of approximately -_ HCl solution. 
 
 By using the factor of normality of this HCl solution, found above
 
 120 QUANTITATIVE ANALYSIS 
 
 N 
 to be 1.108, it is shown that 43.65 c.c. of this approximately -^ HC1 
 
 is equivalent to 48.36 c.c. of exact HC1 solution. 
 
 AQ C)f* 
 
 ' = 1.209, the factor of normality for the approximately 
 ~ NaOH solution. 
 
 The amount of approximately half-normal solution used can 
 always be expressed in terms of the exactly half-normal solution 
 by multiplying the number of cubic centimeters used by the factor 
 of its normality. 
 
 If a solution is not exactly normal, the factor of its normality 
 should be written on the label.
 
 VOLUMETRIC ANALYSIS 121 
 
 (5) The Determination with Iceland Spar* of the Absolute Value of 
 the Approximately Half -Normal Solution of Hydrochloric Acid 
 
 and 
 
 The Preparation of an Exactly Half-Normal Solution of 
 Hydrochloric Add 
 
 (a) The solution of the Iceland spar, CaCOs, in an excess of 
 the approximately half-normal solution of hydrochloric 
 acid. 
 
 (6) The titrating back of the excess of acid with the approxi- 
 mately half-normal solution of sodium hydroxid. 
 
 (c) The addition of the calculated amount of distilled water 
 to the approximately half-normal solution of hydro- 
 chloric acid. 
 
 REACTIONS 
 
 (I) CaC0 3 + 2 HC1 = CaCl 2 + H 2 O+ CO 2 . 
 (II) HC1 4- NaOH = NaCl + H 2 O. 
 
 * If their purity and value is guaranteed, sodium carbonate or precipitated 
 calcium carbonate may be used instead of Iceland spar.
 
 122 QUANTITATIVE ANALYSIS 
 
 THE DETERMINATION OF THE ABSOLUTE VALUE 
 
 Pure calcium carbonate (Iceland spar) requires, of course, an 
 exact amount of hydrochloric acid to dissolve it. The acid can 
 therefore be standardized against it. 
 
 PROCEDURE 
 
 Weigh into Erlenmeyer or ordinary flasks 9l weighing and dis- 
 two portions of about 0.5 of a gram each solvin s the i*iand 
 
 spar in a definite 
 
 of Iceland spar that has been ground to volume of hydro- 
 an impalpable powder. 92 chloric acid 
 
 N 
 Add about 30 c.c. of the -= HC1 from the buret, make a note of 
 
 the exact amount added. 
 
 Let this stand till the Iceland spar is wholly dissolved. Hold to 
 the light to see if there are any particles undissolved. 
 (While the Iceland spar is dissolving, begin to grind the iron 
 ore according to the directions under "The Volumetric 
 Determination of Iron in an Ore," page 150.) 
 
 EXPLANATORY FACTS 
 
 91. If dissolved in a flask, loss by effervescence is avoided. 
 If, however, it is necessary to use a beaker, keep it covered. As 
 the CaCO 3 is somewhat slow to dissolve, fall-strength acid solu- 
 tion acts as a better solvent. 
 
 92. Gritty particles dissolve slowly and with difficulty. Failure 
 to dissolve completely the Iceland spar will result in error and will 
 ruin subsequent analyses.
 
 VOLUMETRIC ANALYSIS 123 
 
 Add two or three drops of the methyl orange indicator and wash 
 down the inside of the flask with water from a wash bottle. 
 
 Make the initial reading on the NaOH buret and run in the 
 NaOH till the indicator shows that the so- Titrating back the 
 lution has just become alkaline. excess of acid 
 
 Again note the NaOH reading. 
 
 In case there is any doubt as to whether the exact end point was 
 reached, titrate back with the hydrochloric acid and proceed 
 to get an exact end point with the sodium hydroxid. 93 
 
 Make careful readings. 
 
 Calculate the excess of acid which was used and then the amount 
 of acid which combined with the calcium carbonate. This 
 
 N 
 gives the amount of approximately -~ HC1 necessary for 
 
 this reaction. Calculate the theoretical amount of exactly 
 
 N 
 
 -= HC1 necessary for this reaction. A comparison of these 
 
 Zi 
 
 N 
 figures shows how much the approximately -~ HC1 needs 
 
 N 
 diluting to make it exactly -5- . 
 
 N 
 If the student's time admits of the standardization of the -^ 
 
 solution of NaOH against oxalic acid, this standardization must 
 
 N 
 be done before the approximately -^ solution of HC1 is diluted to 
 
 N 
 exactly -~ and while the relative values of the acid and alkali 
 
 EXPLANATORY FACT 
 
 93. ' A certain number of the cubic centimeters of the acid have 
 been used in reacting with the calcium carbonate. The excess 
 of acid above this amount has now been determined by titrating 
 
 back with -~- NaOH solution.
 
 124 QUANTITATIVE ANALYSIS 
 
 solutions are still known. In which case, the acid may be diluted to 
 
 N N 
 
 exactly 77 after the standardization of the approximately -^ NaOH 
 
 & & 
 
 against oxalic acid. Otherwise, proceed with the dilution at this 
 point (Calculation, page 127). 
 
 THE PREPARATION OF THE EXACTLY HALF-NORMAL SOLUTION 
 
 Measure accurately the amount of water to be added to the 
 number of cubic centimeters of standard Dilution of fh9 ap _ 
 solution measured. proximate* 5 HCI 
 
 Add this exact amount from a graduated flask, solutiontom i e an 
 pipet or buret. exactly ? solution 
 
 Shake the solution till thoroughly homogeneous.
 
 VOLUMETRIC ANALYSIS 125 
 
 SAMPLE CALCULATIONS 
 
 FOR THE DETERMINATION OF THE ABSOLUTE VALUE 
 
 AND OF 
 
 N 
 THE QUANTITIES TO MAKE AN EXACTLY -= SOLUTION OF HC1 
 
 N 
 If it takes 40 c.c. of an approximately -^ NaOH solution to 
 
 N 
 neutralize 43.65 c.c. of an approximately -^ HC1 solution, then 1 c.c. 
 
 A 
 
 of ^ NaOH = ^por 1.091 c.c. of ^ HC1 ("Relative Value" of 
 the two solutions). 
 
 Amount of -^ HC1 added to the Iceland Spar = 45.40 c.c. 
 
 N 
 Amount of -^ NaOH used to titrate excess of acid = 10.00 c.c. 
 
 N 
 10.00 c.c. of this approximate -~ NaOH = 10.91 c.c. in terms of 
 
 N 
 this approximate -~ HC1. 
 
 10.91 c.c. of HC1 was neutralized by NaOH. 
 45.40 c.c. 
 10.91 c.c. 
 
 Therefore 34.49 c.c. were used to dissolve the Iceland Spar.
 
 126 QUANTITATIVE ANALYSIS 
 
 ABSOLUTE VALUE 
 
 0.9567 g. CaCO 3 required for solution 34.49 c.c. ^ HC1. 
 
 & 
 
 CaC0 3 + 2 HC1 = CaCl 2 + H 2 O + CO 2 . 
 100.07 (CaC0 3 ) : 72.9 (2 HC1) = 0.9567 : x 
 
 x = 0.6969 gram of HC1. 
 
 That is, 34.49 c.c. contain 0.6969 gram of HC1 and therefore 
 1 c.c. contains 0.0202 gram. 
 
 QUANTITIES TO MAKE AN EXACTLY SOLUTION 
 
 N 
 34.49 c.c. of the approximately ^-HCl solution are needed to 
 
 dissolve 0.9567 gram of CaC0 3 . 
 
 How many cubic centimeters of an exact -~ solution would it 
 take? 
 
 The equation in the foregoing section shows that it takes two 
 molecules of HC1 to dissolve one molecule of CaCO 3 . 
 
 Molecular weight of CaCO 3 = 100.07. 
 
 One-half the molecular weight in grams = 50.035. 
 
 With a normal solution of HC1, a liter (1000 c.c.) is equivalent to 
 50.035 grams of calcium carbonate, therefore a liter of half-normal 
 HC1 is equivalent to 25.017 grams. 
 
 25.017 : 1000 :: 0.9567 : x 
 25.017 x = 956.70 
 x = 38.24 
 
 N 
 It takes, then 38.24 c.c. of an exactly -=- HC1 solution to dissolve 
 
 0.9567 gram of calcium carbonate.
 
 VOLUMETRIC ANALYSIS 127 
 
 Since it took less of the approximately -^ HC1 solution than it 
 would have taken were the solution exactly half normal, it is too 
 strong. 
 
 38.24 
 
 34.49 
 
 3.75 
 
 Every 34.49 c.c. of the approximately ^- HC1 should be diluted 
 with 3.75 c.c. of distilled water to make it exactly semi-normal. 
 If there are 500 c.c. of the approximately ^ HC1, ^^ X 3.75 = 
 54.3 c.c. which is the number of cubic centimeters of water to be 
 added to make the HC1 solution exactly half-normal. 
 
 Fractional volumes should be measured with a buret. Measure- 
 ments may be made by using a measuring flask nearest in size to 
 the volume required and the rest of the volume added from a 
 buret. By filling them as many times as necessary, burets only 
 may be used.
 
 128 QUANTITATIVE ANALYSIS 
 
 (6) The Preparation of Exactly Half-Normal Solution of NaOH 
 from Previously Established Values 
 
 If time is limited, the amount of water required Diluti(m of o^ ap _ 
 
 to be added to the approximately half-normal ^,0,^^ ? NaOH 
 
 solution of NaOH to make it exactly half-normal solutioll to ,^ ke , 
 
 can be calculated from the data already obtained exactly N 8olution 
 as follows: 
 
 1 c.c. ^ NaOH was found to equal 1.091 c.c.^HCl. 
 
 If 34.49 c.c. of approximately -^ HC1 are diluted with 3.75 c.c. 
 of distilled water to make an exactly -~ solution of HC1. then 
 f^f = 31.61 and ^=3.43,0. 
 
 Therefore, in this case, every 31.61 c.c. of approximately -^ NaOH 
 should be diluted with 3.43 c.c. of distilled water to make an exactly 
 2~ solution of NaOH, or, to each cubic centimeter of the remaining 
 solution, add 0.108 of a cubic centimeter of water. 
 
 PROCEDURE 
 
 Dilute the alkali as described under the directions for dilution 
 of the acid.
 
 VOLUMETRIC ANALYSIS 129 
 
 (7) The Determination of the Absolute Value of the Approx- 
 imately Half-Normal Solution af Sodium Hydroxid 
 with Oxalic Acid 
 
 and 
 
 The Preparation of an exactly Half-Normal Solution of 
 Sodium Hydroxid 
 
 (a) The titration of a solution of oxalic acid with the ap- 
 proximately half-normal solution of sodium hydroxid. 
 
 (6) Titration back, with the approximately half-normal solu- 
 tion of hydrochloric acid, of the excess of alkali added. 
 
 (c) Calculation and addition of the necessary amount of dis- 
 tilled water to the approximately half-normal solution 
 of sodium hydroxid. 
 
 REACTIONS 
 
 (I) 2 NaOH + H 2 C 2 4 = Na 2 C 2 O 4 + 2 H 2 O. 
 (II) NaOH + HC1 = NaCl + H 2 O.
 
 130 QUANTITATIVE ANALYSIS 
 
 THE DETERMINATION OF THE ABSOLUTE VALUE 
 PROCEDURE 
 
 Weigh into two casseroles two portions of pure, crystallized 
 
 oxalic acid 9 * (H 2 C 2 O 4 .2 H 2 O) of about 0.8 gram each. 
 Dissolve in about 50 c.c. of water. 
 Heat to boiling and add a few drops of phenolphthalein indicator. 
 
 N 
 Titrate hot with NaOH solution till it pro- Titration of the 
 
 duces a pink color which lasts for a few 
 
 minutes. 
 
 N 
 Add from a half to one cubic centimeter of the -~ HC1 solution 
 
 noting the readings. 
 Bring to a boil. 
 
 EXPLANATORY FACT 
 
 94. If oxalic acid of this exact composition is not available, it 
 may be prepared by Winkler's method (" Uebungen in der Mass- 
 analyse," p. 69) . 500 grams of oxalic acid are dissolved in 500 grams 
 of boiling HC1 (1.07 sp. gr.). It is then allowed to crystallize by 
 stirring the solution in a dish placed in ice water. The crystals 
 are filtered through glass wool and washed with HC1. The yield 
 is then redissolved in boiling hydrochloric acid, crystallized and 
 filtered as before. This time, however, the crystals are washed with 
 a little water and redissolved in just enough boiling water. The 
 crystals obtained by cooling this solution are filtered and washed 
 with water and recrystallized at least twice. The final crystals are 
 then dried over a desiccating agent which must be frequently 
 changed. It is now free from chlorin and mineral matter.
 
 VOLUMETRIC ANALYSIS 131 
 
 N 
 Titrate back with the -^ NaOH solution. 
 
 Calculate the excess of alkali added and then the amount of 
 
 alkali which combined with the oxalic acid. This gives the 
 amount of the a 
 for this reaction. 
 
 N 
 amount of the approximately - NaOH solution necessary 
 
 THE PREPARATION OF AN EXACTLY HALF-NORMAL SOLUTION 
 OF SODIUM HYDROXID 
 
 PROCEDURE 
 
 N 
 Calculate the amount of exactly -~ NaOH solution necessary for 
 
 this reaction. A comparison of these figures shows how 
 
 N 
 much the approximately -77 NaOH needs diluting to make 
 
 i 
 
 it exactly -_
 
 132 QUANTITATIVE ANALYSIS 
 
 SAMPLE CALCULATION 
 FOR THE DETERMINATION OF THE ABSOLUTE VALUE 
 
 AND THE 
 
 DETERMINATION OF THE QUANTITIES TO BE ADDED TO MAKE 
 
 N 
 AN EXACTLY SOLUTION OF NaOH 
 
 When standardized with oxalic acid, 
 
 H 2 C 2 O 4 .2 H 2 O + 2NaOH = Na2C 2 O 4 + 4 H 2 
 126.05 80.02 
 
 Weight of oxalic acid used = 0.7500 gram. 
 
 N 
 Volume required of approximately -^ NaOH used in this titra- 
 
 tion, 20 c.c. 
 
 126.05 : 80.02 = 0.7500 : x 
 
 x = 0.4761 gram NaOH. 
 
 Therefore 0.7500 gram H 2 C 2 O 4 .2 H 2 O requires 0.4761 gram NaOH. 
 Therefore 20 c.c. of this solution contain 0.4761 gram NaOH, 
 and 1 c.c. of this solution contains 0.0238 gram NaOH or this 
 solution contains 23.8 grams NaOH per liter. 
 
 If the solution were exactly half-normal, it would contain 20.004 
 grams NaOH per liter or .020 gram in 1 c.c. 
 
 It is therefore too strong and should have added to it 76.9 c.c. 
 of water according to the following: 
 
 Should there remain 405 c.c. of the solution, let x equal the 
 
 N 
 volume required to make the solution exactly -^ 
 
 Then 405 X 0.238 = x X 0.020. 
 
 x = 481.9 c.c. 
 481. 9 c.c. 405 c.c. = 76.9 c.c., the volume to be added.
 
 VOLUMETRIC ANALYSIS 133 
 
 (8) The Reestablishment of the Relative Values of the two 
 Solutions 
 
 If time permits, the correctness of the preceding work may be 
 verified by the reestablishment of the relative values of the two 
 adjusted solutions, equal volumes of which should now neutralize 
 each other. 
 
 PROCEDURE 
 
 Take an accurately measured volume of from 10 to 20 c.c. of 
 
 either solution. 
 
 Use methyl orange as an indicator. 
 Determine the volume of the other solution necessary to effect 
 
 neutralization.
 
 134 QUANTITATIVE ANALYSIS 
 
 THE VOLUMETRIC DETERMINATION 
 
 OF THE 
 TOTAL ALKALI IN SODA ASH 95 
 
 A Typical Saturation Process 
 
 This method is applicable to the titration of caustic soda, caustic 
 potash, or alkali carbonates. 
 
 Soda ash, NasCOs, etc., is: 
 
 (a) dried to determine the moisture; 
 
 (6) neutralized with standard hydrochloric acid; 
 
 (c) calculated as " total available alkali." 
 
 TYPE REACTIONS 
 
 (I) NasCOs + 2 HC1 = 2 NaCl + H 2 + C0 2 . 
 (II) NaOH + HC1 = NaCl + H 2 O. 
 
 EXPLANATORY FACT 
 
 95. Soda ash is calcined crude sodium carbonate resulting from 
 either the "Le Blanc" or the "Ammonia" process for making 
 soda. It contains a little sodium hydroxid, often traces of sulfids, 
 thiosulfates, sulfites, sulfates, silicates and chlorids. There also 
 may be present alumina and ferric oxid. "Le Blanc" soda has, 
 as its chief impurity, sodium sulfate, while "Ammonia" soda is 
 generally free from caustic soda, (NaOH), sulfid and sulfate, and 
 contains the most chlorid. " Ammonia " soda (sp. g. 0.8) is lighter 
 than " Le Blanc " soda (sp. g. 1.2).
 
 VOLUMETRIC ANALYSIS 135 
 
 PROCEDURE 96 
 
 Weigh an ignited platinum crucible. 
 
 Weigh about 5 grams 97 of the sample into the crucible. 
 
 Heat to dull redness for about twenty minutes. 98 Expelling the mois- 
 
 Cool in a desiccator. ture from the soda 
 
 Weigh and repeat the heating for a few minutes ash 
 
 until a constant weight is reached. 
 Calculate the loss in weight as moisture. 
 Transfer the contents of the crucible to a 500 c.c. (No. 4) beaker. 
 Wash the crucible thoroughly and catch the preparation O f th e 
 
 washings in the beaker. solution of the soda 
 
 Add about 100 c.c. of water and stir. 
 Warm, if necessary, till all is dissolved that will dissolve. 
 Transfer this solution quantitatively through a filter directly 
 
 into a 250 c.c. volumetric flask. patration of the 
 
 Wash the filter paper and insoluble residue solution 
 
 with a stream of hot water from a water bottle till a drop 
 
 of the filtrate gives no further reaction with litmus "paper. 
 
 EXPLANATORY FACTS 
 
 96. In the analysis of soda ash, German alkali manufacturers 
 (1) always ignite the soda ash before determining the per cent, of 
 alkali and calculate the results on the ignited material and (2) 
 they include in the total per cent, of alkalinity, that which is due to 
 the insoluble portion, calcium and magnesium carbonates, ferric 
 oxid, etc., as well as the soluble portion. Since the total insoluble 
 matter (including nonalkaline substances like sand) is very small, 
 there is but slight difference in the percent, of alkalinity in the soda 
 ash whether analyzed by the German or other methods. 
 
 97. In the above determination, an unignited sample is weighed 
 and the soluble alkali only is determined. 
 
 98. If this temperature is exceeded, the mass will fuse.
 
 136 QUANTITATIVE ANALYSIS 
 
 Cool to the "graduation temperature" 99 of the flask and add 
 
 water up to the graduation line. Some of this water that 
 
 is added should be directed down all parts of the inside of 
 
 the neck of the flask to make sure that all of the solution 
 
 is collected in its bulb. 
 Dry the inner neck down to the liquid level, using a filter paper 
 
 rolled around a glass rod. 
 Mix the liquid thoroughly by pouring it back and forth from 
 
 the flask into a dry beaker. 100 Preparation of 
 
 After this keep the flask stoppered. <di uot P*** 
 
 Titrations are to be made with aliquot parts of 50 c.c. each of 
 
 this solution. This amount may be measured in pipets or 
 
 volumetric flasks of this capacity. 
 Rinse twice the selected measuring instrument with a little of 
 
 the solution before the aliquot part is measured. 101 
 Pour the measured 50 c.c. into a clean 250 c.c. flask. 
 Wash out the graduated flask quantitatively into the titrating 
 
 flask. 
 Dilute the 50 c.c. to about 100 c.c. 
 
 EXPLANATORY FACTS 
 
 99. The graduation temperature is usually marked on gradu- 
 ated measuring apparatus. It is about room temperature, that is, 
 60 F., or 17.5 C., a temperature decided upon by Mohr. A 
 true liter is the volume of one thousand grams of water at 4 C. 
 As a more practical unit one thousand grams of water at 17.5 C. 
 is taken and is called the "Mohr Liter." 
 
 100. Since the solution has now been mixed sufficiently to 
 make it homogeneous and since only aliquot parts of it are to be 
 used for titration neither that adhering to the beaker nor that 
 which is to be used for rinsing the pipet or 50 c.c. flask need be 
 considered. 
 
 101. Of course the amount of soda ash in each aliquot part cor- 
 responds to one-fifth of the original weight taken.
 
 VOLUMETRIC ANALYSIS 137 
 
 Add three or four drops of methyl orange solution. 102 
 
 From the buret, after noting the reading, add a slight excess of 
 
 HO. 
 
 N 
 Note the reading and titrate back with -^ NaOH and find 
 
 the point at which a drop of either solution xitration of the 
 
 changes the color from yellow to pinkish aasa ^ ae solution 
 
 red or vice versa. 
 End the titration with the acid. 
 Take readings for both acid and alkali. 
 Repeat this determination with another 50 c.c. of the soda ash 
 
 solution. 
 
 EXPLANATORY FACT 
 
 102. Methyl orange is unaffected by the CO 2 that is liberated 
 when the acid is added to the carbonate. Most indicators show 
 an acid reaction with the C0% which makes the alkali solution 
 appear to be neutralized before such is the case. With such indi- 
 cators the solution must be kept at the boiling point to drive off 
 the CO 2 .
 
 138 QUANTITATIVE ANALYSIS 
 
 SAMPLE CALCULATION 
 
 Weight of soda ash taken = 4.9706. 
 
 Solution made up to 250 c.c.; one-fifth of this, 50 c.c., titrated. 
 4.9706 -5- 5 = 0.9941 gram weight of soda ash in each 50 c.c. 
 
 What is the weight of the gaseous HC1 in 1 c.c. of exactly =- 
 
 HC1? 
 
 HC1 (36.46) 
 
 N 
 How much NaaCOs is equivalent to 1 c.c. of exactly - HC1? 
 
 + 2 HCl = 2 NaCl + H 2 + C0 2 
 106 : 72.92 = x : 0.01823 
 x = 0.0265 gram, 
 
 or 0.0265 gram of NaaCOs is equivalent to 1 c.c. of -^ HCl. 
 
 TlTRATIONS 
 
 39.92 c.c. 2.82 c.c. 
 
 1 c.c. of ^ HCl = 1 c.c. of^NaOH 
 
 39.92 - 2.82 = 37.10 c.c. of HCl actually used to neutralize the 
 
 z 
 
 soda ash. 
 
 N 
 37.10 -jr HCl is equivalent to 
 
 37.10 X 0.0265 = 0.98315 gram of Na 2 C0 3 . 
 What per cent, is 0.98315 of 0.9941? 
 0.98315 
 
 0.9941 
 
 = 98.89 per cent total alkali.
 
 VOLUMETRIC ANALYSIS 139 
 
 THE VOLUMETRIC DETERMINATION OF CHLORIN 
 
 IN AN 
 UNKNOWN SALT 
 
 A Typical Precipitation Process 
 
 The salt is: 
 
 (a) dissolved in water; 
 
 (6) titrated with approximately yrr AgNOa with potassium 
 
 chromate as an indicator; 
 (c) calculated as per cent, of chlorin. 
 
 REACTIONS 
 
 I. MCI + AgN0 3 = AgCl + MNO 3 . ~ 
 
 II. K 2 Cr0 4 + 2AgN0 3 = Ag 2 Cr0 4 + 2 KN0 3 . 
 Red
 
 140 QUANTITATIVE ANALYSIS 
 
 THE DETERMINATION OF CHLORIN 
 PROCEDURE 
 
 Weigh into a six-inch evaporating dish or, if the titration is to 
 be done on a white surface, into a 350 c.c. beaker if pre- 
 ferred, two portions of the unknown salt weighing the 
 of about 0.3 gram each. char * e 
 
 Receive from the instructor about 250 c.c. of approximately 
 YJT silver nitrate solution!, Jr c J which must be poured 
 
 into a perfectly clean but not necessarily dry bottle. This 
 solution must be kept closely stoppered and as much away 
 from the light as possible.
 
 VOLUMETRIC ANALYSIS 141 
 
 N 
 STANDARDIZATION OF THE APPROXIMATELY SOLUTION OP 
 
 SILVER NITRATE TO DETERMINE ITS STRENGTH IN 
 TERMS OF CHLORIN 
 
 Weigh about 0.3 gram of pure fused sodium weighing the 
 chlorid (as a standard). standard salt 
 
 Dissolve in cold water. 103 
 
 N 
 Titrate with the approximately -^.silver nitrate solution using as 
 
 an indicator potassium chromate free from Titration for stand _ 
 
 chlorin. 104 * ardization of the 
 
 Calculate 
 
 (1) the value of 1 o*e of the AgNOs in terms of NaCl, 
 
 (2) the per cent, of Cl in NaCl and 
 
 (3) the value of 1 c.c. of this solution of AgNOs in terms 
 of chlorin. 
 
 In an exactly ^ solution of AgNO 3 , 1 c.c. corresponds to 
 0.003545 gram of Cl. 
 
 EXPLANATORY FACTS 
 
 103. The solution of the salt must be practically neutral, as 
 acids exercise a solvent action on Ag 2 CrO 4 . If present, acids 
 must be neutralized with " chlorin-f ree " sodium carbonate. An 
 excess of alkali, however, is to be avoided, as it will cause a pre- 
 cipitation of Ag 2 C03. 
 
 104. As long as any chlorin remains unprecipitated, no red 
 color forms. The permanent formation of the red A&CrO* indi- 
 cates the end point. 
 
 * " Chemistry of the Metals," Experiments Nos. 51 and 54.
 
 142 QUANTITATIVE ANALYSIS 
 
 PROCEDURE 
 
 Titrate the unknown salt just as the pure 
 sodium chlorid was titrated, using K 2 Cr0 4 
 as an indicator.
 
 VOLUMETRIC ANALYSIS 143 
 
 SAMPLE CALCULATIONS 
 
 Standardization of AgN0 3 Solution 
 
 1. Weight of pure NaCl taken = 0.2603 gram. 
 
 N 
 Approximately AgNO 3 used = 44.70 c.c. 
 
 = 0.005823; 
 
 that is, 1 c.c. of the AgNO 3 solution = 0.005823 gram of NaCl. 
 
 2. The per cent, of chlorin in NaCl = 60.65. 
 
 (The student is to show by calculation in the notebook that 
 this is so.) 
 
 3. 60.65 per cent, of 0.005823 = 0.003532. 
 Therefore, 1 c.c. of AgNO 3 = 0.003532 gram of Cl. 
 
 DETERMINATION 
 
 Weight of unknown salt used = 0.3064 grams. 
 Volume of AgNO 3 used = 42.60 c.c. 
 
 0.003532 X 42.60 
 
 0.3064 
 
 = 49.10 per cent, chlorin.
 
 144 QUANTITATIVE ANALYSIS 
 
 THE VOLUMETRIC DETERMINATION OF IRON 
 
 IN 
 AN ORE 
 
 Iron is: 
 
 (a) converted to ferric chlorid, FeCl 3 , by dissolving the ore 
 in hydrochloric acid; 
 
 (6) changed to ferric sulfate, Fe^SO^s, by evaporation with 
 concentrated sulfuric acid; 
 
 (c) reduced to ferrous sulfate, FeS0 4 , by zinc and by hydrogen; 
 
 N 
 
 (d) titrated with ^. potassium permanganate, KMn0 4 ; 
 
 (e) calculated as per cent, of iron. 
 
 REACTIONS 
 
 I. FeaOs + 6 HC1 = 2 FeCl 3 + 3 H 2 O. 
 II. 2 FeCl 3 + 3 H 2 SO 4 = Fe(SO 4 )8 + 6 HCl. 
 
 III. Zn + H 2 SO 4 = ZnSO 4 + H 2 . 
 
 IV. Fe 2 (SO 4 ) 3 + Zn = ZnSO 4 + 2 FeSO 4 . 
 
 V. Fe 2 (S0 4 ) 3 + H 2 = 2 FeSO 4 + H 2 SO 4 . 
 
 > I 
 
 VI. 10 FeSO 4 + 2 KMnO 4 + 8 H 2 SO 4 
 
 = 5 FU N (SO 4 ) 3 + I&0 4 + 2 MnSO 4 + 8 H 2 O. 
 VII. 10 FeO + 50
 
 VOLUMETRIC ANALYSIS 145 
 
 PREPARATION OP AN JQ SOLUTION OP POTASSIUM PERMAN- 
 GANATE, KMn0 4 (158.03) 
 
 As an oxidizing agent in acid solution, potassium permanganate 
 splits up as follows: 
 
 2 KMnO 4 = K 2 O.2 MnO.O 5 (see reactions VI and VII). 
 
 Each two molecules of KMnC>4 furnish five available oxygen 
 atoms, which are equivalent to ten hydrogen atoms. One molecule 
 of KMnC>4 therefore is equivalent to five atoms of hydrogen. 
 
 The molecular weight of KMnO 4 = 158.03. 
 This expressed in grams = 158.03 grams. 
 
 A normal solution of potassium permanganate used as an oxi- 
 dizing agent contains in one liter 31.60 grams, one-fifth of its 
 
 01 n 
 
 molecular weight in grams. A decinormal solution contains ' 
 or 3.16 grams in one liter. 
 
 PROCEDURE 
 
 N Making the 
 
 Prepare half a liter of an y^ solution of potas- standard solution 
 
 sium permanganate. 
 Warm slightly to aid solution. 
 Filter through asbestos on a Witt plate.
 
 146 QUANTITATIVE ANALYSIS 
 
 STANDARDIZATION OF THE - KMnO 4 SOLUTION 105 
 
 N 
 Rather than make an exact JQ KMnO 4 solution, it is usual 
 
 to standardize it in terms of iron or, if it is more convenient, in 
 terms of any other appropriate substance. 
 
 Use either iron wire or Mohr's salt, FeSO 4 . (NH 4 ) 2 SO 4 .6 H 2 O. 
 If iron wire is used, it must be free from rust and Method of stand- 
 be of a known percentage purity. If Mohr's salt 
 is used, it must be in clear crystals (those that have solution 
 lost no water of crystallization) or those from a sample, the iron 
 content of which has been gravimetrically determined. 
 
 PROCEDURE 
 
 Weigh into two Erlenmeyer flasks two samples of iron wire of 
 
 about 0.25 gram each. 
 
 Pour into each flask 100 c.c. of dilute sulfuric add (1.5). 
 Loosely cover each flask with a one-inch watch glass and warm 
 
 gently till all the iron is dissolved, but do not boil. A few 
 
 flakes of carbon, which can easily be dis- standardization of 
 
 tinguished as such, will remain. 
 
 EXPLANATORY FACT 
 
 105. Solutions of KMnO 4 undergo decomposition in the light. 
 If they are to be preserved they must be kept either in colored 
 glass bottles or in bottles covered with black paper. Even then, 
 frequent standardization is desirable.
 
 VOLUMETRIC ANALYSIS 147 
 
 After the foregoing, to be certain that all the iron is in the ferrous 
 state, proceed as follows: Get ready two glass tubes, bent 
 at an angle of about 45, with the longer limb about 
 twelve inches and the shorter about three inches long. In- 
 sert the short limb into a one-hole rubber Reduction of ^ 
 stopper of proper size for the neck of the oxidized iron to the 
 flask. Support the two flasks with clamps ferrous state 
 on ring stands, inclining them at an angle of 45. When 
 the short limb is inserted into the neck of the flask, the long 
 limb of the glass tube should be vertical. 
 
 Put into each flask a very small amount of solid sodium car- 
 bonate, 106 Na 2 CO 3 . 
 
 Immediately add to each flask a very small amount of "40- 
 mesh," chemically pure granular zinc, 107 and stopper the 
 flask at once.* 
 
 Dip the long end of the tubes into solutions cooling the solution 
 of sodium carbonate contained in small in a nommdizing 
 
 beakers." atmosphere 
 
 Gently warm, but do not boil, the solution in the inclined flask 
 till the zinc is dissolved. 109 
 
 EXPLANATORY FACTS 
 
 106. The carbon dioxide thus evolved will expel air from the 
 flasks. 
 
 107. The introduction of the zinc will cause the reduction to 
 the ferrous state of any iron which might possibly have been 
 oxidized during solution (see reactions IV and V). The presence 
 of zinc sulfate hi the solution (see reaction III) does not affect 
 the titration with potassium permanganate. 
 
 108. Although the hydrogen can escape, yet, since the end of 
 the long tube is sealed by the sodium carbonate solution, any 
 ingress of air is impossible. 
 
 109. As the zinc dissolves, the inclined position of the flask 
 prevents loss by spattering. 
 
 * "Chemistry of the Metals," Experiment No. 156.
 
 148 QUANTITATIVE ANALYSIS 
 
 Allow the flask to become cold. 110 
 
 As soon as the solution is quite cold, it should be at once titrated 
 to a faint pink color with the potassium per- Titration of the 
 manganate solution. 111 * 112 ferrous suifate 
 
 EXPLANATORY FACTS 
 
 110. As the solution in the flask cools, the sodium carbonate 
 solution in the beaker rises in the tube, but the first drop coming 
 into the flask causes effervescence and the liquid is driven back 
 down the tube. This gradual equalization of pressure continues 
 until equilibrium is established. 
 
 111. All solutions titrated with permanganate of potassium must 
 be acid preferably with sulfuric acid in order to keep the 
 manganous oxid in solution. 
 
 112. It is often convenient to have on hand a solution of 
 Mohr's salt a sample of which has been titrated with the KMnO 4 
 solution so that the value of one cubic centimeter of the Mohr's 
 salt solution in terms of the permanganate solution may have 
 been previously established. If the end point should ever be 
 exceeded, the solution may then be "titrated back" with the 
 Mohr's salt solution and allowance made for the KMnO 4 which 
 by mistake was added in excess.
 
 VOLUMETRIC ANALYSIS 149 
 
 SAMPLE CALCULATION 
 
 Weight of iron = 0.2500 gram (99.85 per cent. pure). 
 
 N 
 
 y^KMnO 4 solution used = 31.18 c.c. 
 
 - 2500 31 * 8 - 9985 0.0080. Thatis ' 
 1 c.c. of the KMnC>4 solution is equivalent to 0.0080 gram of iron.
 
 150 QUANTITATIVE ANALYSIS 
 
 DETERMINATION OF THE IRON 
 Preparation of the Ore for Analysis 
 
 It is impossible to dissolve and therefore to analyze an ore of 
 this nature that has not been ground to an impalpable powder too 
 smooth to grit between the teeth. This is often a long and tedious 
 operation and should have been begun before the student has 
 reached this determination (see page 122) . Mortars cut from agate 
 (a form of quartz) must be used. Do not put much Preparation of the 
 more of the ore in the mortar at one time than can ore by B lindia e 
 be held on the tip of a small spatula. When ground to an impal- 
 pable powder, transfer to a weighing tube and grind other portions 
 until at least a gram of the ore is ready. 
 
 PROCEDURE 
 
 Weigh out into porcelain crucibles two portions of the ground 
 ore of about 0.5 gram each. 
 
 Heat these crucibles in the Bunsen flame for about ten min- 
 utes. 113 Roasting the ore 
 
 EXPLANATORY FACT 
 
 113. Iron ores often contain organic matter, which, as it might 
 be later acted upon by the permanganate and vitiate the results, 
 must be destroyed by "roasting." Moreover, it also colors the 
 insoluble residue and makes it difficult to tell when the solution 
 of the ore is complete.
 
 VOLUMETRIC ANALYSIS 151 
 
 Cool the crucibles and transfer their contents to two 250 c.c. 
 casseroles. If all the ore cannot be removed, the crucibles 
 themselves must be put into the casseroles as well. 114 
 
 Add to each sample 25 c.c. of hydrochloric add (1.2 sp. gr.). 
 
 Cover the casseroles and let the ore digest at a temperature just 
 below boiling 115 for from thirty minutes to an hour. This 
 will generally effect complete decomposi- Preparation of the 
 tion as shown by a white residue. If after solution 
 this time the solvent action appears to have ceased and the 
 residue is still dark, proceed as follows: 
 
 Dilute the solution, filter off and wash the residue till the wash- 
 ings give no test for acid. 
 
 Ignite the filter paper and residue in a platinum crucible and 
 fuse 116 the ash with a small quantity of Fusion of any 
 sodium carbonate, Na^COa. insoluble residue 
 
 After cooling, partly fill the crucible with water and cautiously 
 boil. 
 
 EXPLANATORY FACTS 
 
 114. Platinum crucibles must not be put into iron solutions. 
 
 115. The iron oxid in most iron ores, if ground to an impalpable 
 powder, is wholly soluble in strong hydrochloric acid. Hard or 
 prolonged boiling or too great concentration of the solution of 
 FeCls must be avoided to prevent loss of iron. In the laboratories 
 of some steel works, it is customary to leave the ore in the hydro- 
 chloric acid on steam baths over night. The next day the solu- 
 tion is usually complete. Some analysts advocate adding a few 
 drops of nitric acid to hasten the solution. 
 
 116. By fusion, the insoluble substances are transformed into 
 such compounds as silicates of the alkalies, carbonates of the 
 heavy metals, etc. This fused mass is entirely decomposed by 
 treatment with dilute hydrochloric acid. Therefore, any iron 
 which may have remained undissolved by the original treatment 
 with acid is now obtained hi the solution as FeCl 3 .
 
 152 QUANTITATIVE ANALYSIS 
 
 Add this solution and any residue to the original hydrochloric 
 acid solution. 
 
 Carefully wash out the platinum crucible and solution of the 
 add the washings to the solution. fusion 
 
 Warm until effervescence ceases. 
 
 Whether or not this secondary process was needed, a white 
 residue need not be filtered off. 
 
 Add about 5 c.c. of concentrated sulfuric acid to conversion to the 
 the cooled hydrochloric acid solution. suUate 
 
 Evaporate under the hood until fumes of 80s are evolved. 117 
 
 Cool the solution and dilute to about 100 c.c. 
 
 Warm the liquid until nothing but flocculent silica remains 
 undissolved. 
 
 Transfer quantitatively to a 250 c.c. flask. 
 
 Add 5 grams of "40-mesh" C. P. granular zinc and put rubber 
 stoppers carrying the bent glass tubes, as Reduction of the 
 described on page 147, into the flasks. The iron 
 tubes should, as before, dip into the sodium carbonate solu- 
 tion. Avoid hydrogen explosions! 
 
 EXPLANATORY FACT 
 
 117. Potassium permanganate in the presence of hydrochloric 
 acid causes the oxidation of ferrous salts, as will be seen by the 
 following: 
 
 2 KMnO 4 + 10 FeCl 2 + 16 HC1 
 
 = 2 MnCl 2 + 2 KC1 + 10 FeCl 3 + 8H 2 O; 
 
 but it is also true that 
 
 2 KMn0 4 + 16 HC1 = 2 KC1 + 2 MnCl 2 + 5 C1 2 + 8 H 2 O. 
 
 The titration with permanganate, then, in the presence of hydro- 
 chloric acid, is attended with a possibility of loss unless special 
 precaution, such as adding MnSO 4 , etc., is taken. It is therefore 
 customary to remove all the hydrochloric acid by means of this 
 evaporation with sulfuric acid (see reaction II).
 
 VOLUMETRIC ANALYSIS 153 
 
 Allow the zinc to dissolve entirely. Aid the process at the last 
 
 by a gentle heat. Do not boil. 
 With the tubes still sealed by the sodium carbonate solution, 
 
 allow the solutions to cool. The action cooiingthe 
 
 will be the same as described on page 148. solution 
 When cool, 118 the solution should be at once xitration of the 
 
 titrated with the standardized perman- 5nm 
 
 ganate solution. 
 
 EXPLANATORY FACT 
 
 118. The complete reduction may be tested for as follows: With- 
 draw a minute drop of the solution on the end of a "drawn out" 
 glass rod and touch it to a drop of KSCN solution on the white 
 tile of the buret stand. If no red color forms, the reduction is 
 complete. If a red color does appear, more zinc must be added 
 and the process repeated.
 
 154 QUANTITATIVE ANALYSIS 
 
 SAMPLE CALCULATION 
 
 Weight of ore used = 0.5603 gram. 
 KMnO 4 solution used = 32.68 c.c. 
 
 Standardization of KMnO 4 solution is 0.0080 of gram of iron 
 (see page 149). 
 
 32.68 X 0.0080 = 0.2614 gram of iron "in 0.5306 gram of ore. 
 0.2614 
 
 0.5306 
 
 = 49.26 per cent, of iron.
 
 VOLUMETRIC ANALYSIS 
 
 155 
 
 FACTORS NEEDED FOR THE DETERMINATIONS IN GRAVIMETRIC 
 WORK INCLUDED IN THIS BOOK* 
 
 Determina- 
 tion of 
 
 Weighed as, 
 
 Required. 
 
 Factor. 
 
 Log. 
 
 Al 
 
 A1 2 3 
 
 Al 
 
 0.53033 
 
 1.72455 
 
 Cu 
 
 CuO 
 
 Cu 
 
 0.79891 
 
 1.90250 
 
 Fe 
 
 FeaOs 
 
 Fe 
 
 0.69944 
 
 1.84475 
 
 S0 4 
 
 BaS0 4 
 
 SO 4 
 
 0.41155 
 
 1.61442 
 
 Cl 
 
 AgCl 
 
 Cl 
 
 0.24738 
 
 1.39337 
 
 MgO 
 
 Mg2P 2 7 
 
 MgO 
 
 0. 36219 
 
 1.55894 
 
 * Other factors, if needed, may be found in Olsen's Chemical Annual, in the 
 1 Chemiker Kalender," or Treadwell'a " Quantitative Analysis."
 
 156 
 
 QUANTITATIVE ANALYSIS 
 
 INTERNATIONAL ATOMIC WEIGHTS 
 
 Aluminum 
 
 Al 
 
 0=16 
 27.1 
 120.2 
 39.9 
 75.0 
 137.37 
 208.0 
 11.0 
 79.92 
 112.40 
 132.81 
 40.07 
 12.00 
 140.25 
 35.46 
 52.1 
 58.97 
 93.5 
 63.57 
 162.5 
 167.7 
 152.0 
 19.0 
 157.3 
 69.9 
 72.5 
 9.1 
 197.2 
 4.0 
 1.008 
 114.8 
 126.92 
 193.1 
 55.84 
 82.9 
 139.0 
 207.1 
 7.0 
 174.0 
 24.32 
 54.93 
 200.6 
 
 Molybdenum 
 Neodymium 
 Neon 
 
 ...Mo 
 ...Nd 
 
 ...Ne 
 
 = 16 
 
 96.0 
 144.3 
 20.0 
 58.68 
 14.01 
 190.9 
 16.00 
 106.' 
 31.0 
 195.0 
 39.1 
 140.6 
 226.4 
 102.9 
 85.45 
 101.7 
 150.4 
 44.1 
 79.2 
 28.3 
 107.88 
 23.00 
 87.62 
 32.07 
 181.5 
 127.5 
 159.2 
 204.0 
 232.42 
 168.5 
 119.0 
 48.1 
 184.0 
 238.5 
 51.06 
 128.0 
 
 172.0 
 89.0 
 65.37 
 90.6 
 
 
 Sb 
 
 
 A 
 
 
 .As 
 .Ba 
 Ri 
 
 Nickel 
 
 ...Ni 
 
 B " 
 
 Nitrogen 
 
 ...N 
 
 Bismuth 
 
 Osmium 
 Oxygen 
 Palladium 
 
 ...Os 
 ...O 
 ...Pd 
 
 Boron 
 
 B 
 
 
 Rr 
 
 
 Cd 
 
 Phosphorus 
 
 ...P 
 
 
 Cs 
 
 Platinum 
 
 . ...Pt 
 
 Calcium 
 
 .Ca 
 .C 
 Ce 
 
 Potassium 
 Praseodymium . . . 
 Radium 
 
 ...K 
 ...Pr 
 .. .Ra 
 
 Carbon 
 
 Chlorin 
 
 .Cl 
 .Cr 
 .Co 
 .Cb 
 Cn 
 
 Rhodium 
 Rubidium 
 Ruthenium 
 Samarium 
 
 ...Rh 
 ...Rb 
 . ..Ru 
 
 ...Sa 
 
 Chromium 
 Cobalt .... 
 
 Columbium 
 
 Scandium 
 
 ...Sc 
 Se 
 
 Dysprosium 
 Erbium 
 
 Dy 
 F,r 
 
 Selenium . . 
 
 Silicon 
 Silver 
 Sodium 
 
 ...Si 
 ...Ag 
 
 Na 
 
 Europium 
 Fluorin 
 
 .Eu 
 .F 
 Gd 
 
 Strontium 
 
 ...Sr 
 
 
 .Ga 
 .Ge 
 .Gl 
 An 
 
 Sulphur 
 Tantalum 
 
 ...S 
 ...Ta 
 
 
 
 Tellurium 
 
 Te 
 
 Gold 
 
 Terbium 
 Thallium 
 Thorium 
 Thulium 
 
 ...Tb 
 
 ...Tl 
 ...Th 
 ...Tm 
 
 Helium 
 
 .He 
 .H 
 .In 
 .1 
 Tr 
 
 Hydrogen 
 
 lodin 
 Indium 
 
 Tin 
 
 ...Sn 
 ...Ti 
 ...W 
 ...U 
 
 Titanium 
 Tungsten 
 Uranium 
 
 
 Fe 
 
 
 Kr 
 
 Lanthanum 
 Lead 
 
 .La 
 .Pb 
 T,i 
 
 Vanadium 
 
 v 
 
 Xenon 
 
 ...Xe 
 ter- 
 ...Yb 
 
 Ytterbium (Neoyl 
 bium) 
 
 
 .Lu 
 Mg 
 .Mn 
 Hg 
 
 Magnesium 
 Manganese 
 Mercury 
 
 Yttrium 
 
 ...Y 
 ...Zn 
 ...Zr 
 
 Zinc 
 Zirconium 
 

 
 LOGARITHMS 
 
 157 
 
 LOGARITHMS 
 
 -1 
 
 
 
 
 
 
 
 
 
 
 
 Proportional Parts. 
 
 11 
 
 
 
 1 
 
 - 
 
 
 
 
 
 
 
 
 133 
 
 456 
 
 8 9 
 
 10 
 
 0000 
 
 3043 
 
 0086 
 
 0128 
 
 170 
 
 212 
 
 0253 
 
 3294 
 
 0334 
 
 0374 
 
 4 8 12 
 
 7 21 25 
 
 9 33 37 
 
 11 
 
 0414 
 
 453 
 
 0492 
 
 0531 
 
 569 
 
 607 
 
 0645 
 
 3682 
 
 0719 
 
 0755 
 
 4 8 11 
 
 5 19 23 
 
 6 30 34 
 
 12 
 
 0792 
 
 828 0864 
 
 0899 
 
 0934 
 
 969 
 
 1004 
 
 1038 
 
 1072 
 
 1106 
 
 3 7 10 
 
 4 17 21 
 
 4 28 31 
 
 13 
 
 139 
 
 173 1206 
 
 1239 
 
 271 
 
 303 1335 
 
 1367 
 
 1399 
 
 1430 
 
 3 6 10 
 
 3 16 19 
 
 3 26 29 
 
 14 
 
 1461 
 
 492 1523 
 
 1553 
 
 584 
 
 614 
 
 1644 
 
 1673 
 
 1703 
 
 1732 
 
 369 
 
 2 15 18 
 
 & 24 27 
 
 15 
 
 1761 
 
 790 818 
 
 1847 
 
 875 
 
 9031931 
 
 1959 
 
 1987 
 
 2014 
 
 368 
 
 1 14 17 
 
 20 22 25 
 
 16 
 
 2041 
 
 01 is 
 
 2095 
 
 2122 
 
 2148 
 
 1752201 
 
 2227 
 
 2253 
 
 2279 
 
 358 
 
 1 13 16 
 
 8 21 24 
 
 17 
 
 2304 
 
 :;:;n 
 
 2355 
 
 2380 
 
 2405 
 
 430:2455 
 
 2480 
 
 2504 
 
 2529 
 
 2 7 
 
 12 15 
 
 7 20 22 
 
 18 
 
 2553 
 
 577 
 
 2601 
 
 2625 
 
 2648 
 
 672:2695 
 
 2718 
 
 2742 
 
 2765 
 
 2 7 
 
 9 12 14 
 
 6 19 21 
 
 19 
 
 2788 
 
 2810 
 
 2833 
 
 2856 
 
 2878 
 
 900 
 
 2923 
 
 2945 
 
 2967 
 
 2989 
 
 2 7 
 
 9 11 13 
 
 6 18 20 
 
 20 
 
 3010 
 
 3032 
 
 3054 
 
 3075 
 
 3096 
 
 118 
 
 3139 
 
 3160 
 
 3181 
 
 3201 
 
 2 6 
 
 8 11 13 
 
 5 17 19 
 
 21 
 
 3222 
 
 3243 
 
 3263 
 
 3284 
 
 3304 
 
 32413345 
 
 3365 
 
 3385 
 
 3404 
 
 2 6 
 
 8 10 12 
 
 4 16 18 
 
 22 
 
 3424 
 
 3444 
 
 3464 
 
 3483 
 
 3502 
 
 522 3541 
 
 3560 
 
 3579 
 
 ;:,<;>s 
 
 2 6 
 
 8 10 12 
 
 4 15 17 
 
 23 
 
 3617 
 
 3636 
 
 3655 
 
 3674 
 
 3692 
 
 711 3729 
 
 3747 
 
 3766 
 
 3784 
 
 2 6 
 
 7 9 11 
 
 3 15 17 
 
 24 
 
 3802 
 
 3820 
 
 3838 
 
 3856 
 
 3874 
 
 892 3909 
 
 3927 
 
 3945 
 
 3962 
 
 2 5 
 
 7 9 11 
 
 12 14 16 
 
 25 
 
 3979 
 
 3997 
 
 4014 
 
 4031 
 
 4048 
 
 4065 4082 
 
 4099 
 
 4116 
 
 4133 
 
 235 
 
 7 9 10 
 
 12 14 15 
 
 26 
 
 4150 
 
 4166 
 
 4183 
 
 4200 
 
 4216 
 
 4232 '4249 
 
 4265 
 
 4281 
 
 4298 
 
 235 
 
 7 8 10 
 
 11 13 15 
 
 27 
 
 4314 
 
 4330 
 
 4346 
 
 4362 
 
 4378 
 
 4393 [4409 
 
 4425 
 
 4440 
 
 4456 
 
 235 
 
 689 
 
 11 13 14 
 
 28 
 
 4472 
 
 4487 
 
 4502 
 
 4518 
 
 4533 
 
 4548 4564 
 
 4579 
 
 4594 
 
 4609 
 
 2 3 5 
 
 689 
 
 11 12 14 
 
 29 
 
 4624 
 
 4639 
 
 4654 
 
 4669 
 
 4683 
 
 4698 4713 
 
 4728 
 
 4742 
 
 4757 
 
 1 3 4 
 
 679 
 
 10 12 13 
 
 30 
 
 4771 
 
 4786 
 
 4800 
 
 4814 
 
 4829 
 
 4843 4857 
 
 4871 
 
 4886 
 
 4900 
 
 1 3 4 
 
 6 9 
 
 10 11 13 
 
 31 
 
 4914 
 
 4928 
 
 4942 
 
 4955 
 
 4969 
 
 4983 4997 
 
 5011 
 
 5024 
 
 5038 
 
 1 3 4 
 
 6 8 
 
 10 11 12 
 
 32 
 
 5051 
 
 5065 
 
 5079 
 
 5092 
 
 5105 
 
 5119'5132 
 
 5145 
 
 5159 
 
 5172 
 
 1 3 4 
 
 5 8 
 
 9 11 12 
 
 33 
 
 5185 
 
 5198 
 
 5211 
 
 5224 
 
 5237 
 
 52505263 
 
 5276 
 
 5289 
 
 5302 
 
 1 3 4 
 
 5 8 
 
 9 10 12 
 
 34 
 
 5315 
 
 5328 
 
 5340 
 
 5353 
 
 5366 
 
 5378.5391 
 
 5403 
 
 5416 
 
 5428 
 
 1 3 4 
 
 5 8 
 
 9 10 11 
 
 35 
 
 5441 
 
 5453 
 
 5465 
 
 5478 
 
 5490 
 
 5502 5514 
 
 5527 
 
 5539 
 
 5551 
 
 1 2 4 
 
 5 7 
 
 9 10 11 
 
 36 
 
 5563 
 
 5575 
 
 5587 
 
 5599 
 
 5611 
 
 5623 
 
 563" 
 
 5647 
 
 5658 
 
 5670 
 
 1 2 4 
 
 5 7 
 
 8 10 11 
 
 37 
 
 5682 
 
 5694 
 
 5705 
 
 5717 
 
 5729 
 
 5740 5752 
 
 5763 
 
 5775 
 
 5786 
 
 1 2 3 
 
 5 7 
 
 8 9 10 
 
 38 
 
 5798 
 
 5809 
 
 5821 
 
 5832 
 
 5843 
 
 5855 5866 
 
 5877 5888 
 
 5899 
 
 1 2 3 
 
 5 7 
 
 8 9 10 
 
 39 
 
 5911 
 
 5922 
 
 5933 
 
 5944 
 
 5955 
 
 5966 5977 
 
 5988 
 
 5999 
 
 6010 
 
 1 2 3 
 
 457 
 
 8 9 10 
 
 40 
 
 6021 
 
 6031 
 
 6042 
 
 6053 
 
 6064 
 
 60756085 
 
 6096 6107 
 
 6117 
 
 1 2 3 
 
 5 6 
 
 8 9 10 
 
 41 
 
 6128 
 
 6138 
 
 6149 
 
 6160 
 
 6170 
 
 6180,6191 
 
 6201 6212 
 
 6222 
 
 1 2 3 
 
 5 6 
 
 7 8 9 
 
 42 
 
 6232 
 
 6243 
 
 6253 
 
 6263 
 
 6274 
 
 628416294 
 
 6304 6314 
 
 6325 
 
 1 2 3 
 
 5 6 
 
 7 8 
 
 43 
 
 6335 
 
 6345 
 
 6355 
 
 6365 
 
 6375 
 
 6385 6395 
 
 64056415 
 
 6425 
 
 1 2 3 
 
 5 6 
 
 7 8 
 
 44 
 
 6435 
 
 6444 
 
 6454 
 
 6464 
 
 6474 
 
 6484 6493 
 
 65036513 
 
 6522 
 
 1 2 3 
 
 5 6 
 
 7 8 
 
 45 
 
 6532 
 
 6542 
 
 6551 
 
 6561 
 
 657 
 
 6580 6590 
 
 65996609 
 
 6618 
 
 1 2 3 
 
 5 6 
 
 7 8 
 
 46 
 
 6628 
 
 6637 
 
 6646 
 
 6656 
 
 6660 
 
 66756684 
 
 6693 6702 
 
 6712 
 
 1 2 3 
 
 5 6 
 
 7 7 
 
 47 
 
 6721 
 
 6730 
 
 6739 
 
 6749 
 
 6758 
 
 6767 
 
 6771 
 
 6785 6794 
 
 6803 
 
 1 2 3 
 
 5 5 
 
 6 7 
 
 48 
 
 6812 
 
 6821 
 
 6830 
 
 6839 
 
 6848 
 
 6857 6866 
 
 6875 
 
 (iSS 
 
 6893 
 
 1 2 3 
 
 4 5 
 
 678 
 
 49 
 
 6902 
 
 6911 
 
 6920 
 
 6928 
 
 693 
 
 6946 6955 
 
 6964 6972 
 
 698 
 
 1 2 3 
 
 4 5 
 
 678 
 
 ~50~ 
 
 6990 
 
 6998 
 
 7007 
 
 7016 
 
 702 
 
 7033 
 
 7042 
 
 7050705E 
 
 7067 
 
 1 2 3 
 
 3 5 
 
 678 
 
 51 
 
 52 
 
 7076 
 7160 
 
 7084 
 7168 
 
 7093 
 7177 
 
 710 
 
 7185 
 
 711 
 
 719 
 
 7118 
 7205 
 
 7126 
 
 7210 
 
 713c 
 
 7218 
 
 7143 
 7226 
 
 7152 
 
 7235 
 
 1 2 3 
 122 
 
 3 5 
 3 5 
 
 678 
 
 677 
 
 53 
 
 7243 
 
 7251 
 
 725S 
 
 7267 
 
 727 
 
 7284 
 
 [7292 
 
 730C 
 
 7308 
 
 731 
 
 1 2 2 
 
 3 5 
 
 667 
 
 54 
 
 7324 
 
 7332 
 
 734C 
 
 7348 
 
 735 
 
 736^ 
 
 [7372 
 
 738C 
 
 17388 
 
 739 
 
 1 2 2 
 
 3 5 
 
 667
 
 158 
 
 QUANTITATIVE ANALYSIS 
 
 LOGARITHMS Continued 
 
 -J 
 II 
 
 55 
 56 
 57 
 
 58 
 59 
 
 60 
 61 
 62 
 63 
 64 
 
 ~65~ 
 66 
 67 
 
 68 
 69 
 
 70 
 71 
 
 72 
 73 
 74 
 
 ~75~ 
 76 
 
 77 
 78 
 79 
 
 80 
 81 
 82 
 83 
 
 84 
 
 
 
 1 
 
 7412 
 7490 
 7566 
 7642 
 7716 
 
 7789 
 7860 
 7931 
 8000 
 8069 
 
 It 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7451 
 7528 
 7604 
 7679 
 7752 
 
 7825 
 7896 
 7966 
 3035 
 3102 
 
 3169 
 3235 
 8299 
 8363 
 8426 
 
 8488 
 8549 
 8609 
 
 siifiO 
 8727 
 
 8785 
 8842 
 8899 
 8954 
 9009 
 
 9063 
 9117 
 9170 
 9222 
 9274 
 
 7 
 
 7459 
 7536 
 7612 
 7686 
 7760 
 
 7832 
 7903 
 7973 
 8041 
 8109 
 
 8176 
 8241 
 8306 
 8370 
 8432 
 
 8494 
 8555 
 8615 
 8675 
 8733 
 
 8 
 
 7466 
 7543 
 7619 
 7694 
 7767 
 
 7839 
 7910 
 7980 
 8048 
 8116 
 
 g 
 
 Proportional Parts. 
 
 
 133 
 
 456 
 
 789 
 
 "404 
 7482 
 7559 
 7634 
 7/09 
 
 7782 
 7853 
 7924 
 7993 
 8062 
 
 7419 
 
 7497 
 7574 
 7649 
 7723 
 
 7796 
 7868 
 7938 
 8007 
 8075 
 
 7427 
 7505 
 7582 
 7657 
 7731 
 
 7803 
 
 7875 
 7945 
 8014 
 8082 
 
 7435 
 7513 
 7589 
 7664 
 
 7738 
 
 7810 
 7882 
 7952 
 8021 
 8089 
 
 7443 
 7520 
 7597 
 7672 
 7745 
 
 818 
 889 
 959 
 028 
 096 
 
 7474 
 7551 
 7627 
 7701 
 
 7774 
 
 7846 
 7917 
 7987 
 8055 
 8122 
 
 2 
 2 
 2 
 
 2 
 2 
 2 
 2 
 2 
 
 3 5 
 3 5 
 3 5 
 3 4 
 3 4 
 
 3 4 
 3 4 
 334 
 334 
 334 
 
 5 6 7 
 5 6 7 
 567 
 5 6 7 
 567 
 
 566 
 6 6 
 6 6 
 5 6 
 5 6 
 
 8129 
 8195 
 8261 
 8325 
 8388 
 
 8451 
 8513 
 
 fel 
 
 8692 
 
 8136 
 8202 
 8267 
 8331 
 8395 
 
 8457 
 8519 
 
 8579 
 8639 
 8698 
 
 8142 
 8209 
 8274 
 8338 
 8401 
 
 8463 
 8525 
 8585 
 8645 
 8704 
 
 8149 
 8215 
 8280 
 8344 
 8407 
 
 8470 
 8531 
 8591 
 8651 
 8710 
 
 8156 
 
 8222 
 8287 
 8351 
 8414 
 
 8476 
 8537 
 8597 
 8657 
 8716 
 
 162 
 
 8228 
 8293 
 8357 
 8420 
 
 8482 
 8543 
 8603 
 8663 
 
 8722 
 
 8182 
 8248 
 8312 
 8376 
 8439 
 
 8500 
 8561 
 8621 
 8681 
 8739 
 
 8189 
 8254 
 8319 
 8382 
 8445 
 
 8506 
 
 s,-,ii7 
 8627 
 8686 
 8745 
 
 2 
 2 
 2 
 2 
 2 
 
 2 
 
 2 
 2 
 
 334 
 334 
 334 
 334 
 234 
 
 234 
 234 
 234 
 234 
 234 
 
 5 
 5 
 
 fi 
 5 
 5 
 5 
 5 
 
 8751 
 8808 
 8865 
 8921 
 8976 
 
 9031 
 9085 
 9138 
 9191 
 9243 
 
 8756 
 8814 
 8871 
 8927 
 8982 
 
 9036 
 
 9090 
 9143 
 9196 
 9248 
 
 9299 
 9350 
 9400 
 9450 
 9499 
 
 9547 
 9595 
 9643 
 9689 
 9736 
 
 9782 
 9827 
 9872 
 9917 
 9961 
 
 8762 
 8820 
 8876 
 8932 
 8987 
 
 9042 
 9096 
 9149 
 9201 
 9253 
 
 8768 
 8825 
 8882 
 8938 
 8993 
 
 9047 
 9101 
 9154 
 9206 
 9258 
 
 8774 
 8831 
 8887 
 8943 
 8998 
 
 9053 
 9106 
 9159 
 9212 
 9263 
 
 8779 
 8837 
 8893 
 8949 
 9004 
 
 9058 
 9112 
 9165 
 9217 
 9269 
 
 8791 
 8848 
 8904 
 8960 
 9015 
 
 9069 
 9122 
 9175 
 9227 
 9279 
 
 8797 
 8854 
 8910 
 8965 
 9020 
 
 9074 
 9128 
 9180 
 9232 
 9284 
 
 9335 
 9385 
 9435 
 9484 
 9533 
 
 9581 
 9628 
 9675 
 9722 
 9768 
 
 8802 
 8859 
 8915 
 8971 
 9025 
 
 9079 
 9133 
 9186 
 9238 
 9289 
 
 2 
 2 
 2 
 2 
 2 
 
 2 
 2 
 2 
 2 
 2 
 
 233 
 233 
 233 
 233 
 233 
 
 233 
 233 
 
 233 
 2 3 3 
 
 5 
 5 
 5 
 5 
 5 
 
 5 
 5 
 5 
 5 
 5 
 
 85 
 86 
 87 
 88 
 89 
 
 90 
 91 
 92 
 93 
 94 
 
 9294 
 9345 
 9395 
 9445 
 9494 
 
 9542 
 9590 
 9638 
 9685 
 9731 
 
 9304 
 9355 
 9405 
 9455 
 9504 
 
 9552 
 9600 
 9647 
 9694 
 9741 
 
 9786 
 9832 
 9877 
 9921 
 996 
 
 9309 
 9360 
 9410 
 9460 
 9509 
 
 9557 
 9605 
 9652 
 9699 
 9745 
 
 9315 
 9365 
 9415 
 9465 
 9513 
 
 9562 
 9609 
 9657 
 9703 
 9750 
 
 9320 
 9370 
 9420 
 9469 
 9518 
 
 9566 
 9614 
 9661 
 9708 
 9754 
 
 9325 
 9375 
 9425 
 9474 
 9523 
 
 9571 
 9619 
 9666 
 9713 
 9759 
 
 9330 
 9380 
 9430 
 9479 
 9528 
 
 9576 
 9624 
 9671 
 9717 
 9763 
 
 9340 
 9390 
 9440 
 9489 
 9538 
 
 9586 
 9633 
 9680 
 9727 
 9773 
 
 2 
 
 2 
 
 
 .0 
 
 
 
 
 
 
 
 233 
 233 
 223 
 223 
 223 
 
 2 2 
 2 2 
 2 2 
 2 2 
 2 2 
 
 4 5 
 4 5 
 3 
 3 
 3 
 
 3 
 3 
 3 
 3 
 3 
 
 95 
 96 
 97 
 98 
 99 
 
 9777 
 9823 
 9868 
 9912 
 9956 
 
 9791 
 9836 
 9881 
 992C 
 996 
 
 9795 
 9841 
 9886 
 9930 
 9974 
 
 9800 
 
 9845 
 9890 
 9934 
 9978 
 
 9805 
 9850 
 9894 
 9939 
 9983 
 
 9809 
 9854 
 9899 
 9943 
 9987 
 
 9814 
 9859 
 9903 
 9948 
 9991 
 
 9818 
 9863 
 9908 
 9952 
 9996 
 
 
 
 
 
 
 
 223 
 223 
 223 
 223 
 223 
 
 3 
 3 
 3 
 3 4 
 3 3
 
 LOGARITHMS 
 
 159 
 
 LOGARITHMS. Continued 
 
 2 
 
 aS 
 
 SI 
 
 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 Proportional Parts. 
 
 
 
 
 .00 
 .01 
 .02 
 .03 
 .04 
 
 .05 
 
 .06 
 .07 
 .08 
 .09 
 
 1000 
 1023 
 1047 
 1072 
 1096 
 
 1122 
 1148 
 1175 
 1202 
 1230 
 1259 
 1288 
 1318 
 1349 
 1380 
 
 1413 
 1445 
 1479 
 1514 
 1549 
 1585 
 1622 
 1660 
 1698 
 1738 
 
 1778 
 1820 
 1862 
 1905 
 1950 
 
 1002 
 1026 
 1050 
 1074 
 1099 
 
 1125 
 1151 
 1178 
 1205 
 1233 
 1262 
 1291 
 1321 
 1352 
 1384 
 
 1416 
 1449 
 1483 
 1517 
 1552 
 1589 
 1626 
 1663 
 1702 
 1742 
 
 1782 
 1824 
 1866 
 1910 
 1954 
 
 1005 
 1028 
 1052 
 1076 
 1102 
 
 1127 
 1153 
 1180 
 1208 
 1236 
 1265 
 1294 
 1324 
 1355 
 1387 
 
 1419 
 1452 
 1486 
 1521 
 1556 
 1592 
 1629 
 1667 
 1706 
 1746 
 
 1786 
 1828 
 1871 
 1914 
 1959 
 
 1007 
 1030 
 1054 
 1079 
 1104 
 
 1130 
 1156 
 1183 
 1211 
 1239 
 1268 
 1297 
 1327 
 1358 
 1390 
 
 1422 
 1455 
 1489 
 1524 
 1560 
 
 1009 
 1033 
 1057 
 1081 
 1107 
 
 1132 
 1159 
 1186 
 1213 
 1242 
 1271 
 1300 
 1330 
 1361 
 1393 
 
 1426 
 1459 
 1493 
 1528 
 1563 
 1600 
 1637 
 1675 
 1714 
 1754 
 
 1795 
 1837 
 1879 
 1923 
 1968 
 
 1012 
 1035 
 1059 
 1084 
 1109 
 
 1135 
 1161 
 1189 
 1216 
 1245 
 1274 
 1303 
 1334 
 1365 
 1396 
 
 1429 
 1462 
 1496 
 1531 
 1567 
 1603 
 1641 
 1679 
 1718 
 1758 
 
 1799 
 1841 
 1884 
 1928 
 1972 
 
 1014 
 1038 
 1062 
 1086 
 1112 
 
 1138 
 1164 
 1191 
 1219 
 1247 
 
 1016 
 1040 
 1064 
 1089 
 1114 
 
 1140 
 1167 
 1194 
 1222 
 1250 
 
 1019 
 1042 
 1067 
 1091 
 1117 
 
 1143 
 1169 
 1197 
 1225 
 1253 
 1282 
 1312 
 1343 
 1374 
 1406 
 
 1439 
 1472 
 1507 
 1542 
 1578 
 1614 
 1652 
 1690 
 1730 
 1770 
 
 1811 
 1854 
 1897 
 1941 
 1986 
 
 1021 
 1045 
 1069 
 1094 
 1119 
 
 1146 
 1172 
 1199 
 1227 
 1256 
 1285 
 1315 
 1346 
 1377 
 1409 
 
 1442 
 1476 
 1510 
 1545 
 1581 
 1618 
 1656 
 1694 
 1734 
 1774 
 
 1816 
 1858 
 1901 
 1945 
 1991 
 
 
 
 
 
 1 
 
 
 
 
 
 
 
 1 
 1 
 1 
 1 
 2 
 
 2 
 2 
 2 
 2 
 2 
 
 2 2 
 2 2 
 2 2 
 2 2 
 2 2 
 
 222 
 222 
 222 
 223 
 223 
 
 .10 
 .11 
 .12 
 .13 
 .14 
 
 .15 
 
 .16 
 .17 
 .18 
 .19 
 
 1276 
 1306 
 1337 
 1368 
 1400 
 
 1432 
 1466 
 1500 
 1535 
 1570 
 1607 
 1644 
 1683 
 1722 
 1762 
 
 1803 
 1845 
 1888 
 1932 
 1977 
 
 1279 
 1309 
 1340 
 1371 
 1403 
 
 1435 
 1469 
 1503 
 1538 
 1574 
 1611 
 1648 
 1687 
 1726 
 1766 
 
 1807 
 1849 
 1892 
 1936 
 1982 
 
 
 
 
 1 
 1 
 
 1 
 
 
 
 
 
 1 2 
 
 2 2 
 2 2 
 2 2 
 
 2 2 
 
 2 2 
 2 2 
 2 2 
 
 223 
 223 
 223 
 233 
 233 
 
 233 
 233 
 233 
 233 
 333 
 
 .20 
 .21 
 .22 
 .23 
 .24 
 
 .25 
 
 .26 
 .27 
 .28 
 .29 
 
 1596 
 1633 
 1671 
 1710 
 1750 
 
 1791 
 
 1832 
 1875 
 1919 
 1963 
 
 
 
 
 
 
 
 
 
 
 
 
 
 2 2 
 222 
 222 
 222 
 
 222 
 223 
 223 
 223 
 223 
 
 333 
 333 
 333 
 3 3 
 3 3 
 
 3 
 3 
 3 
 
 .30 
 .31 
 .32 
 .33 
 .34 
 
 .35 
 
 .36 
 .37 
 .38 
 .39 
 
 1995 
 2042 
 2089 
 2138 
 2188 
 
 2239 
 2291 
 2344 
 2399 
 2455 
 
 2000 
 2046 
 2094 
 2143 
 2193 
 
 2244 
 2296 
 2350 
 2404 
 2460 
 
 2004 2009 
 2051 2056 
 2099 2104 
 21482153 
 21982203 
 
 22492254 
 23012307 
 23552360 
 241012415 
 2466 2472 
 
 2014 
 2061 
 2109 
 2158 
 2208 
 
 2259 
 2312 
 2366 
 2421 
 
 2477 
 
 2018 
 2065 
 2113 
 2163 
 2213 
 
 2265 
 2317 
 2371 
 
 2427 
 2483 
 
 2023 
 2070 
 2118 
 2168 
 2218 
 
 2270 
 2323 
 2377 
 2432 
 2489 
 
 2028 
 2075 
 2123 
 2173 
 2223 
 
 2275 
 2328 
 2382 
 2438 
 2495 
 
 2032 
 2080 
 2128 
 
 2178 
 2228 
 
 2280 
 2333 
 2388 
 2443 
 2500 
 
 2037 
 2084 
 2133 
 2183 
 2234 
 
 2286 
 2339 
 2393 
 2449 
 2506 
 
 
 
 
 
 
 1 
 
 2 
 2 
 
 223 
 223 
 223 
 223 
 233 
 
 2 3 
 2 3 
 2 3 
 2 3 
 2 3 
 
 
 .40 
 .41 
 .42 
 .43 
 .44 
 
 .45 
 .46 
 .47 
 .48 
 .49 
 
 2512 
 2570 
 2630 
 2692 
 2754 
 
 2818 
 2884 
 2951 
 3020 
 3090 
 
 2518 
 2576 
 2636 
 2698 
 2761 
 
 2825 
 2891 
 2958 
 3027 
 3097 
 
 2523 
 2582 
 2642 
 2704 
 2767 
 
 2831 
 
 2897 
 2965 
 3034 
 3105 
 
 2529 
 2588 
 2649 
 2710 
 2773 
 
 2838 
 2904 
 2972 
 3041 
 3112 
 
 2535 
 2594 
 2655 
 2716 
 2780 
 
 2844 
 2911 
 2979 
 3048 
 3119 
 
 2541 
 2600 
 2661 
 2723 
 2786 
 
 2851 
 2917 
 2985 
 3055 
 3126 
 
 2547 
 2606 
 2667 
 2729 
 2793 
 
 2858 
 2924 
 2992 
 3062 
 3133 
 
 2553 
 2612 
 2673 
 2735 
 2799 
 
 2864 
 2931 
 2999 
 3069 
 3141 
 
 2559 
 2618 
 2679 
 2742 
 2805 
 
 2871 
 2938 
 3006 
 3076 
 3148 
 
 2564 
 2624 
 2685 
 2748 
 2812 
 
 2877 
 2944 
 3013 
 3083 
 3155 
 
 2 
 
 2 
 2 
 2 
 2 
 
 2 
 2 
 2 
 2 
 2 
 
 2 3 
 2 3 
 2 3 
 3 3 
 3 3 
 
 3 3 
 3 3 
 3 3 
 3 4 
 3 4 
 
 5 
 
 5 
 6 
 6 
 5 6 
 
 556 
 556 
 556 
 566 
 566
 
 160 
 
 QUANTITATIVE ANALYSIS 
 
 LOGARITHMS Concluded 
 
 A 
 
 m 
 
 
 
 1 
 
 2 
 
 3 
 
 4 
 
 5 
 
 6 
 
 7 
 
 8 
 
 9 
 
 Proportional Parts. 
 
 123 
 
 456 
 
 789 
 
 .50 
 .51 
 .52 
 .53 
 .54 
 
 .55 
 .56 
 57 
 .58 
 .59 
 
 3162 
 3236 
 3311 
 
 3388 
 3467 
 
 3548 
 3631 
 3715 
 3802 
 3890 
 
 3170 
 3243 
 3319 
 3396 
 3475 
 
 3556 
 3639 
 3724 
 3811 
 3899 
 3990 
 4083 
 4178 
 4276 
 4375 
 
 4477 
 4581 
 4688 
 4797 
 4909 
 
 3177 
 3251 
 3327 
 3404 
 3483 
 
 3565 
 3648 
 3733 
 3819 
 3908 
 
 3184 
 3258 
 3334 
 3412 
 3491 
 
 3573 
 3656 
 3741 
 3828 
 3917 
 
 3192 
 3266 
 3342 
 3420 
 3499 
 
 3581 
 3664 
 3750 
 3837 
 3926 
 
 3199 
 3273 
 3350 
 
 3428 
 3508 
 
 3589 
 3673 
 3758 
 3846 
 
 !!() 
 
 3206 
 3281 
 3357 
 3436 
 3516 
 
 3597 
 3681 
 3767 
 3855 
 3945 
 
 3214 
 3289 
 3365 
 3443 
 3524 
 
 3606 
 3690 
 3776 
 3864 
 3954 
 
 3221 
 3296 
 3373 
 3451 
 3532 
 
 3614 
 3698 
 3784 
 3873 
 3963 
 
 3228 
 3304 
 3381 
 3459 
 3540 
 
 3622 
 3707 
 3793 
 3882 
 3972 
 
 2 2 
 2 2 
 2 2 
 2 2 
 
 2 2 
 2 3 
 
 344 
 345 
 345 
 
 567 
 
 567 
 567 
 
 
 
 345 
 345 
 
 677 
 678 
 
 2 3 
 2 3 
 
 4 5 
 5 5 
 
 678 
 678 
 
 .60 
 .61 
 .62 
 .63 
 .64 
 
 .65 
 .66 
 .67 
 .68 
 .69 
 
 3981 
 4074 
 4169 
 4266 
 4365 
 
 4467 
 4571 
 4677 
 4786 
 4898 
 
 3999 
 4093 
 4188 
 4285 
 4385 
 
 4487 
 4592 
 4699 
 4808 
 4920 
 
 4009 
 4102 
 4198 
 4295 
 4395 
 
 4498 
 4603 
 4710 
 4819 
 4932 
 
 4018 
 4111 
 4207 
 4305 
 4406 
 
 4508 
 4613 
 4721 
 4831 
 4943 
 
 4027 
 4121 
 4217 
 4315 
 4416 
 
 4519 
 
 4624 
 4732 
 4842 
 4955 
 
 4036 
 4130 
 4227 
 4325 
 4426 
 
 4529 
 4634 
 4742 
 4853 
 4966 
 
 4046 
 4140 
 4236 
 4335 
 4436 
 
 4539 
 4645 
 4753 
 4864 
 4977 
 5093 
 5212 
 5333 
 5458 
 5585 
 
 5715 
 5848 
 5984 
 6124 
 6266 
 
 4055 
 4150 
 4246 
 4345 
 4446 
 
 4550 
 4656 
 4764 
 4875 
 4989 
 5105 
 5224 
 5346 
 5470 
 5598 
 
 5728 
 5861 
 5998 
 6138 
 6281 
 
 4064 
 4159 
 4256 
 4355 
 
 2 3 
 2 3 
 2 3 
 2 3 
 
 5 6 
 5 6 
 5 6 
 456 
 
 678 
 789 
 789 
 789 
 
 4560 
 4667 
 4775 
 4887 
 5000 
 5117 
 5236 
 5358 
 5483 
 5610 
 
 5741 
 5875 
 6012 
 6152 
 6295 
 
 2 3 
 2 3 
 2 3 
 2 3 
 
 456 
 456 
 457 
 467 
 567 
 
 7 8 9 
 7 9 10 
 8 9 10 
 8 9 10 
 8 9 10 
 
 .70 
 .71 
 .72 
 .73 
 .74 
 
 .75 
 
 .76 
 .77 
 .78 
 .79 
 
 5012 
 5129 
 5248 
 5370 
 5495 
 
 5623 
 5754 
 5888 
 6026 
 6166 
 
 5023 
 5140 
 5260 
 5383 
 5508 
 
 5636 
 5768 
 5902 
 6039 
 6180 
 
 5035 
 5152 
 5272 
 5395 
 5521 
 
 5649 
 5781 
 5916 
 6053 
 6194 
 
 5047 
 5164 
 5284 
 5408 
 5534 
 
 5662 
 5794 
 5929 
 6067 
 6209 
 
 5058 
 5176 
 5297 
 5420 
 5546 
 
 5675 
 5808 
 5943 
 6081 
 6223 
 
 5070 
 5188 
 5309 
 5433 
 5559 
 
 5689 
 5821 
 5957 
 6095 
 6237 
 
 5082 
 5200 
 5321 
 5445 
 5572 
 
 5702 
 5834 
 5970 
 6109 
 6252 
 
 2 4 
 2 4 
 2 4 
 3 4 
 3 4 
 
 3 4 
 3 4 
 3 4 
 3 4 
 3 4 
 
 567 
 567 
 567 
 568 
 568 
 
 578 
 578 
 578 
 678 
 679 
 
 8 9 11 
 8 10 11 
 10 11 
 10 11 
 10 12 
 
 10 12 
 11 12 
 10 11 12 
 10 11 13 
 10 11 13 
 
 .80 
 .81 
 .82 
 .83 
 .84 
 
 .85 
 .86 
 .87 
 .88 
 .89 
 .90 
 .91 
 .92 
 .93 
 .94 
 
 .95 
 .96 
 .97 
 .98 
 .99 
 
 6310 
 6457 
 6607 
 6761 
 6918 
 
 7079 
 7244 
 7413 
 7586 
 7762 
 7943 
 8128 
 8318 
 8511 
 8710 
 
 8913 
 9120 
 9333 
 9550 
 
 9772 
 
 6324 
 6471 
 6622 
 6776 
 6934 
 
 7096 
 7261 
 7430 
 7603 
 7780 
 
 6339 
 6486 
 6637 
 6792 
 6950 
 
 7112 
 
 7278 
 7447 
 7621 
 7798 
 7980 
 8166 
 8356 
 8551 
 8750 
 
 8954 
 9162 
 9376 
 9594 
 9817 
 
 6353 
 6501 
 6653 
 6808 
 6966 
 
 7129 
 7295 
 7464 
 7638 
 7816 
 7998 
 8185 
 8375 
 8570 
 8770 
 
 8974 
 9183 
 9397 
 9616 
 9840 
 
 6368 
 6516 
 6668 
 6823 
 6982 
 
 7145 
 7311 
 7482 
 7656 
 7834 
 80l7 
 8204 
 8395 
 8590 
 8790 
 
 8995 
 9204 
 9419 
 9638 
 9863 
 
 6383 
 6531 
 6683 
 6839 
 6998 
 
 7161 
 7328 
 7499 
 7674 
 7852 
 
 6397 
 6546 
 6699 
 6855 
 7015 
 
 7178 
 7345 
 7516 
 7691 
 
 7870 
 
 6412 
 6561 
 6714 
 6871 
 7031 
 
 7194 
 7362 
 7534 
 7709 
 7889 
 
 6427 
 6577 
 6730 
 6887 
 7047 
 
 7211 
 7379 
 7551 
 
 7727 
 7907 
 
 6442 
 6592 
 6745 
 6902 
 7063 
 
 7228 
 7396 
 7568 
 7745 
 7925 
 
 134 
 235 
 235 
 235 
 235 
 
 235 
 235 
 235 
 2 5 
 2 5 
 
 679 
 689 
 689 
 689 
 6 8 10 
 
 7 8 10 
 7 8 10 
 7 9 10 
 7 9 11 
 7 9 11 
 
 10 12 13 
 11 12 14 
 11 12 14 
 11 13 14 
 11 13 15 
 
 12 13 15 
 
 12 13 15 
 12 14 16 
 12 14 16 
 13 14 16 
 
 7962 
 8147 
 8337 
 8531 
 8730 
 
 8933 
 9141 
 9354 
 9572 
 9795 
 
 8035 
 8222 
 8414 
 8610 
 8810 
 
 9016 
 9226 
 9441 
 9661 
 
 fese 
 
 8054 
 8241 
 8433 
 8630 
 8831 
 
 9036 
 9247 
 9462 
 9683 
 9908 
 
 8072 
 8260 
 8453 
 8650 
 8851 
 
 9057 
 9268 
 9484 
 9705 
 9931 
 
 8091 
 
 8279 
 8472 
 8670 
 8872 
 
 9078 
 9290 
 9506 
 9727 
 9944 
 
 8110 
 
 8299 
 8492 
 8690 
 8892 
 
 9099 
 9311 
 9528 
 9750 
 9977 
 
 2 6 
 2 6 
 2 6 
 2 6 
 2 6 
 
 2 6 
 2 6 
 2 7 
 2 7 
 257 
 
 7 9 11 
 8 9 11 
 8 10 12 
 8 10 12 
 8 10 12 
 
 8 10 12 
 8 11 13 
 9 11 13 
 9 11 13 
 9 11 14 
 
 13 15 17 
 13 15 17 
 14 15 17 
 14 16 18 
 14 16 18 
 
 15 17 19 
 15 17 19 
 15 17 20 
 16 18 20 
 16 18 20
 
 INDEX 
 
 Absolute value of a standard hydrochloric acid solution, determination of. 121 
 
 Acidimetry 112 
 
 Aliquot part 90, 136 
 
 Alkalimetry 112 
 
 Alkalinity, total, of soda ash, determination of 134 
 
 Alloy for electrolytic determination 89 
 
 Aluminium, determination of, in alum 33 
 
 removal of, from dolomite 71 
 
 Analysis, gravimetric and volumetric, compared 2, 97 
 
 Anode 86 
 
 Apparatus 5 
 
 for measuring volume of liquids 98 
 
 Balances 10 
 
 adjustment of 11 
 
 Barium sulfate, precipitating and filtering of 59 
 
 Baths, air and steam 7 
 
 Burets f .. 99 
 
 reading of 100 
 
 Calcium, determination of, in a mineral 73 
 
 Calcium oxalate, purification of 74 
 
 Calculation 27 
 
 Calibration of apparatus for measuring volume 98 
 
 Cathode and cation 86 
 
 Checking of weights by instructor 16, 30 
 
 Chlorin, gravimetric determination of, in a soluble salt 62 
 
 volumetric determination of, in a soluble salt 139 
 
 161
 
 162 INDEX 
 
 Cleaning volumetric glassware 101 
 
 Constant weight 26 
 
 Coolers for reduced iron solutions 117 
 
 Copper in an alloy, electrolytic determination of 92 
 
 determination of, in copper sulfate 45 
 
 sulfate, preparation of pure crystals of *. . . 46 
 
 oxid, method of igniting 49 
 
 Crucibles 7 
 
 cleaning of 8 
 
 Gooch 25 
 
 Current density 86 
 
 Decantation 23 
 
 Desiccators 10 
 
 use of 41 
 
 Dissociation 20, 85 
 
 Dolomite (or similar minerals), analysis of 68 
 
 Electrodes 86 
 
 drying of 92 
 
 Electrolysis 86 
 
 Electrolyte 86 
 
 Electrolytic Analysis 85-94 
 
 Electrolytic determinations 87 
 
 End point, determination of 103 
 
 Evaporations 7, 24 
 
 Factors, calculation and use of 27, 155 
 
 for approximately normal solutions 119 
 
 Filter flasks 7 
 
 Filtering 22 
 
 Filter paper 5, 22 
 
 for barium sulfate 60 
 
 tared 25 
 
 Filtration, arrangement of apparatus for 36 
 
 Funnels 6 
 
 Fusion of insoluble substances 17, 79 
 
 Gibbs, Wolcott, method of, for magnesium 76 
 
 Glassware, cleaning of surface of, in volumetric analysis 101 
 
 Gooch crucibles 25 
 
 Gravimetric Analysis 33-81 
 
 definition of . . 12
 
 INDEX 163 
 
 Hydrochloric acid, preparation of half-normal solution of 113 
 
 determination of absolute value of solution of. 121 
 
 dilution of solution of, to an exact value 124, 127 
 
 Iceland spar, use of, as a standard 122 
 
 Ignition of precipitates 25 
 
 Indicators 105 
 
 Ions 20, 85 
 
 Iron, gravimetric determination of, in a soluble salt 53 
 
 volumetric determination of, in a soluble salt 144 
 
 and SO 4 , separation of 55, 58 
 
 removal of, from dolomite 71 
 
 Isolation of elements or radicals ... 17 
 
 Lacmoid 107 
 
 Liquid level, reading of 99, 100 
 
 Litmus 106 
 
 Magnesium, determination of, in dolomite 76 
 
 Magnesium oxalate, properties of 74 
 
 Magnesium ammonium phosphate, ignition of, to magnesium pyrophos- 
 
 phate 77 
 
 Manganese, removal of, from dolomite 71 
 
 Measuring flasks 99 
 
 Meniscus 99, 100 
 
 Methyl orange 106 
 
 Microcosmic salt, use of, for the determination of magnesium 76 
 
 Normal solutions 108 
 
 adjustment of, by dilution to an exact volume 124, 127, / 
 
 128, 132 * 
 Notebooks. . . 30 
 
 Permanency of standard solutions Ill 
 
 Phenolphthalein 107 
 
 Pipets 98 
 
 Platinum, rules for use of 8 
 
 "Policeman," use of, for removing precipitates 5, 38 
 
 Potassium cyanid, use of 89, 90 
 
 Potassium permanganate, preparation and standardization of a tenth- 
 normal solution of ... 145
 
 164 INDEX 
 
 PAGE 
 
 Precipitates, drying of 7, 39, 40 
 
 ignition of 25, 40 
 
 purification of 18 
 
 washing of 17, 20 
 
 Precipitation 17, 20 
 
 Qualitative and quantitative analysis, comparison of 1 
 
 Quills, use of, for removing precipitates 38 
 
 Radical SO 4 , gravimetric determination of, in a soluble salt 57 
 
 Reagents 17 
 
 amounts of, to add. 18 
 
 Records, types of 31, 43 
 
 Relative values of acid and alkali solutions, determination of 116 
 
 Separation of elements or radicals 17 
 
 Silica, determination of, in minerals and rocks 78 
 
 purification of, by hydrofluoric acid 81 
 
 removal of, from dolomite 70 
 
 from iron ore 151 
 
 Silicates, fusion of, to accomplish solution 17, 79 
 
 Silicic acid, dehydration of 70, 80 
 
 Silver, electrolytic determination of 91 
 
 Silver chlorid, action of light upon 63, 66 
 
 method of igniting 65 
 
 Silver nitrate, standardization of a solution of 141, 143 
 
 Soda ash, determination of total alkalinity of 134 
 
 Sodium hydroxid, dilution of a solution of, to exact value .... 128, 131, 132 
 
 preparation of a half-normal solution of 115 
 
 standardization of, against oxalic acid 129 
 
 Solubilities, table of 21 
 
 Solution, process of 17 
 
 Solutions, facts regarding 19 
 
 homogeneity of 19 
 
 Solvents 19 
 
 Standard solutions 102 
 
 permanency of Ill, 115 
 
 dilution of, to exact value 121, 125 
 
 Study outside the laboratory 32 
 
 Suction for filtrations 7, 22 
 
 Sulfuric acid, determination of, in a soluble salt 57 
 
 Tared filter papers 25 
 
 Titration . . 102
 
 INDEX 165 
 
 PAGE 
 
 Volumetric Analysis 97-154 
 
 definition of 97 
 
 Washing of precipitates 22, 37, 38 
 
 test for the completion of 22 
 
 Washing by decantation 23, 37 
 
 Weighing, directions for 15 
 
 precautions for 13 
 
 Weighing tubes 6 
 
 Weights, analytical 11 
 
 average approximate 15 
 
 constant 26 
 
 Work, planning of 29 
 
 Zero point, determination of 14 
 
 Zinc, "40-mesh," use of, to reduce iron in volumetric determination. . . 147 
 
 Printed in the United States of America. 
 
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 This book is DUE on the last date stamped below. 
 
 
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 JIW6 1949 
 
 
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 RE 
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 Form L9-10m-3,'48(A79^| 
 
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