IKLF 
 
 OM1C THEORY, 
 
 PA;PERS, 
 
 LAM H\ '- ; VV'-, M j A^-Vt ?^, M. 
 THOMAS THOMSON, M.i), 
 
 Blcmbic Ciu 
 
 No. 2. 
 
(gfemfitc fu6 (geprtnf0 (Ho. 2. 
 
 FOUNDATIONS 
 
 OF THE 
 
 ATOMIC THEORY: 
 
 COMPRISING 
 
 PAPERS AND EXTRACTS 
 
 BY 
 
 JOHN DALTON, 
 WILLIAM HYDE WOLL'ASTON, M.D. 
 
 AND 
 
 THOMAS THOMSON, M.D., 
 
 (1802-1808.) 
 
 A/H>X 
 
 OF THE r \ 
 
 UNIVERSITY) 
 ^/ 
 
 EDINBURGH : 
 WILLIAM F. CLAY, 18 TEVIOT PLACE. 
 
 LONDON : 
 
 SIMPKIN, MARSHALL, HAMILTON, KENT & CO. LTD. 
 1893. 
 
PREFACE. 
 
 THIS little book contains reprints of original memoirs 
 and extracts from text-books, embracing the 
 earliest publications by their respective authors bearing 
 upon the foundation of the Atomic Theory. 
 
 The view is pretty generally held by chemists that it 
 was in the endeavour to explain numerous examples 
 which were known to him, of that general regularity 
 which is now commonly called Jthe Law of Multiple 
 Proportions, that Dalton was led to entertain the ideas 
 which he held regarding the constitution of compound 
 bodies. There has therefore been included, along with 
 later publications, the paper by Dalton in which there is 
 described probably the first example of this regularity 
 with which he became acquainted. 
 
 The first part of Dalton's " New System of Chemical 
 Philosophy," containing his own account of his views, did 
 not appear until 1808, although these views had been 
 embodied in courses of lectures which Dalton had 
 delivered some years previously. The earliest printed 
 account of his views is that given by Dr Thomas Thomson 
 in Volume 3 of the Third Edition of his "System of 
 Chemistry," published in 1807. This account is repro- 
 duced in the following pages. 
 
 A paper by Wollaston on Super-acid and Sub-acid 
 Salts, giving various examples illustrative of the Law of 
 Multiple Proportions, is also included. 
 
 L. D. 
 
*SE 
 OF THE 
 :VERSITY 
 
 EXPERIMENTAL ENQUIRY INTO THE 
 PROPORTION OF THE SEVERAL 
 GASES OR ELASTIC FLUIDS, CON- 
 STITUTING THE ATMOSPHERE. BY 
 JOHN DALTON.* 
 
 Read Nov. 12, 1802. 
 
 IN a former paper which I submitted to this Society, 
 " On the constitution of mixed gases," I adopted 
 such proportions of the simple elastic fluids to constitute 
 the atmosphere as were then current, not intending to 
 warrant the accuracy of them all, as stated in the said 
 paper; my principal object in that essay was, to point I 
 out the manner in which mixed elastic fluids exist \ 
 together, and to insist upon what I think a very important 
 and fundamental position in the doctrine of such fluids : 
 namely, that the elastic or repulsive power of each 
 particle is confined to those of its own kind ; and con- 
 sequently the force of such fluid, retained in a given 
 vessel, or gravitating, is the same in a separate as in a 
 mixed state, depending upon its proper density and 
 temperature. This principle accords with all experience, 
 and I have no doubt will soon be perceived and acknow- 
 ledged by chemists and philosophers in general ; and its 
 application will elucidate a variety of facts, which are 
 otherwise involved in obscurity. 
 
 * From the Memoirs of the Literary and Philosophical Society 
 of Manchester, Second Series, Volume I., 1805, pp. 244-258. In 
 this paper there is announced the first example of the law of multiple 
 proportions. 
 
6 Dalton. 
 
 The objects of the present essay are, 
 
 1. To determine the weight of each simple atmosphere, 
 abstractedly ; or, in other words, what part of the weight 
 of the whole compound atmosphere is due to azote ; 
 what to oxygen, &c. &c. 
 
 2. To determine the relative weights of the different 
 gases in a given volume of atmospheric air, such as it is 
 at the earth's surface. 
 
 3. To investigate the proportions of the gases to each 
 other, such as they ought to be found at different eleva- 
 tions above the earth's surface. 
 
 To those who consider the atmosphere as a chemical 
 compound, these three objects are but one . others, who 
 adopt my hypothesis, will see they are essentially distinct. 
 With respect to the first : It is obvious, that, on my 
 hypothesis, the density and elastic force of each gas at 
 the earth's surface, are the effects of the weight of the 
 atmosphere of that gas solely, the different atmospheres 
 not gravitating one upon another. Whence the first 
 object will be obtained by ascertaining what share of 
 elastic force is due to each gas in a given volume of the 
 compound atmosphere ; or, which amounts to the same 
 thing, by finding how much the given volume is 
 diminished under a constant pressure, by the abstraction 
 of each of its ingredients singly. Thus, if it should 
 appear that by extracting the oxygenous gas from any 
 mass of atmospheric air, the whole was diminished \ in 
 bulk, still being subject to a pressure of 30 inches of 
 mercury ; then it ought to be inferred that the oxygenous 
 atmosphere presses the earth with a force of 6 inches of 
 mercury, &c. 
 
 In order to ascertain the second point, it will be 
 further necessary to obtain the specific gravity of each 
 gas ; that is, the relative weights of a given volume of 
 each in a pure state, subject to the same pressure and 
 
Proportion of Gases in the Atmosphere. 7 
 
 temperature. For, the weight of each gas in any given 
 portion of atmospheric air, must be in the compound 
 ratio of its force and specific gravity. 
 
 With respect to the third object, it may be observed, 
 that those gases which are specifically the heaviest must 
 decrease in density the quickest in ascending. If the 
 earth's atmosphere had been a homogeneous elastic fluid 
 of the same weight it is, but ten times the specific gravity, 
 it might easily be demonstrated that no sensible portion 
 of it could have arisen to the summits of the highest 
 mountains. On the other hand, an atmosphere of hydro- 
 genous gas, of the same weight, would support a column 
 of mercury nearly 29 inches on the summit of Mount 
 Blanc. 
 
 The several gases constantly found in every portion 
 of atmospheric air, and in such quantities as are capable 
 of being appreciated, are azotic, oxygenous, aqueous 
 vapour, and carbonic acid. It is probable that hydro- 
 genous gas also is constantly present ; but in so small 
 proportion as not to be detected by any test we are 
 acquainted with ; it must therefore be confounded in the 
 large mass of azotic gas. 
 
 i. Of the Weight of the Oxygenous and Azotic 
 Atmospheres. 
 
 Various processes have been used to determine the 
 quantity of oxygenous gas. 
 
 1. The mixture of nitrous gas and air over water. 
 
 2. Exposing the air to liquid sulphuret of potash or 
 lime, with or without agitation. 
 
 3. Exploding hydrogen gas and air by electricity. 
 
 4. Exposing the air to a solution of green sulphat or 
 muriat of iron in water, strongly impregnated with nitrous 
 gas. 
 
8 Dalton. 
 
 5. Burning phosphorus in the air. 
 
 In all these cases the oxygen enters into combination 
 and loses its elasticity ; and if the several processes be 
 conducted skilfully, the results are precisely the same 
 from all. In all parts of the earth and at every season of 
 the year, the bulk of any given quantity of atmospheric 
 air appears to be reduced nearly 2 1 per cent, by abstract- 
 ing its oxygen. This fact, indeed, has not been generally 
 admitted till lately ; some chemists having found, as they 
 apprehended, a great difference in the quantity of oxygen 
 in the air at different times and places; on some occasions 
 20 per cent, and on others 30, and more of oxygen are 
 said to have been found. This I have no doubt was 
 owing to their not understanding the nature of the 
 operation and of the circumstances influencing it. 
 Indeed it is difficult to see, on any hypothesis, how a 
 disproportion of these two elements should ever subsist 
 in the atmosphere. 
 
 As the first of the processes above-mentioned has 
 been much discredited by late authors, and as it appears 
 from my experience to be not only the most elegant and 
 expeditious of all the methods hitherto used, but also as 
 correct as any of them, when properly conducted, I shall, 
 on this occasion, animadvert upon it. 
 
 1. Nitrous gas may be obtained pure by nitric acid 
 diluted with an equal bulk of water poured upon copper 
 or mercury ; little or no artificial heat should be applied. 
 The last product of gas this way obtained, does not con- 
 tain any sensible portion of azotic gas ; at least it may 
 easily be got with less than 2 or 3 per cent, of that gas : 
 It is probably nearly free from nitrous oxide also, when 
 thus obtained. 
 
 2. If 100 measures of common air be put to 36 of 
 pure nitrous gas in a tube 3-ioth of an inch wide and 5 
 inches long, after a few minutes the whole will be reduced 
 
Proportion of Gases in the Atmosphere. 9 
 
 to 79 or 80 measures, and exhibit no signs of either 
 oxygenous or nitrous gas. 
 
 3. If 100 measures of common air be admitted to 72 
 of nitrous gas in a wide vessel over water, such as to form 
 a thin stratum of air, and an immediate momentary 
 agitation be used, there will, as before, be found 79 or 80 
 measures of pure azotic gas for a residuum. 
 
 4. If, in the last experiment, less than 72 measures of 
 nitrous gas be used, there will be a residuum containing 
 oxygenous gas ; if more, then some residuary nitrous gas 
 will be found. 
 
 These facts clearly point out the theory of the process: 
 the elements of oxygen may combine with a certain 
 portion of nitrous gas, or with twice that portion, but with 
 no intermediate quantity. In the former case nitric acid 
 is the result ; in the latter nitrous acid : but as both these 
 may be formed at the same time, one part of the oxygen 
 going to one of nitrous gas, and another to two, the 
 quantity of nitrous gas absorbed should be variable ; from 
 36 to 72 per cent, for common air. This is the principal 
 cause of that diversity which has so much appeared in 
 the results of chemists on this subject. In fact, all the 
 gradation in quantity of nitrous gas from 36 to 72 may 
 actually be observed with atmospheric air of the same 
 purity ; the wider the tube or vessel the mixture is made 
 in, the quicker the combination is effected, and the more 
 exposed to water, the greater is the quantity of nitrous 
 acid and the less of nitric that is formed. 
 
 To use nitrous gas for the purpose of eudiometry 
 therefore, we must attempt to form nitric acid or nitrous 
 wholly, and without a mixture of the other. Of these the 
 former appears from my experiments to be most easily 
 and most accurately effected. In order to this a narrow 
 tube is necessary ; one that is just wide enough to let air 
 pass water without requiring the tube to be agitated, is 
 
IO Dalton. 
 
 best. Let little more nitrous gas than is sufficient to 
 form nitric acid be admitted to the oxygenous gas ; let 
 no agitation be used ; and as soon as the diminution 
 appears to be over for a moment let the residuary gas be 
 transferred to another tube, and it will remain without 
 any further diminution of consequence. Then T 7 of the 
 loss will be due to oxygen. The transferring is necessary 
 to prevent the nitric acid formed and combined with the 
 water, from absorbing the remainder of the nitrous gas to 
 form nitrous acid. 
 
 Sulphuret of lime is a good test of the proportion of 
 oxygen in a given mixture, provided the liquid be not 
 more than 20 or 30 per cent, for the gas (atmospheric 
 air) ; if the liquid exceed this, there is a portion of azotic 
 gas imbibed somewhat uncertain in quantity. 
 
 Volta's eudiometer is very accurate as well as elegant 
 and expeditious: according to Monge, TOO oxygen require 
 196 measures of hydrogen; according to Davy 192 ; but 
 from the most attentive observations of my own, 185 are 
 sufficient. In atmospheric air I always find 60 per cent, 
 diminution when fired with an excess of hydrogen ; that 
 is, 100 common air with 60 hydrogen, become 100 after 
 the explosion, and no oxygen is found in the residuum ; 
 here 21 oxygen take 39 hydrogen. 
 
 2. Of the Weight of the Aqueous Vapour Atmosphere. 
 
 I have, in a former essay, (Manchester Mem. vol. 5. 
 p. 2, page 559.) given a table of the force of vapour in 
 vacuo for every degree of temperature, determined by 
 experiment ; and in the sequel of the essay, have shown 
 that the force of vapour in the atmosphere is the very 
 same as in vacuo, when they are both at their utmost for 
 any given temperature. To find the force of aqueous 
 vapour in the atmosphere, therefore, we have nothing 
 
Proportion of Gases in the A tmosphere. 1 1 
 
 more to do than to find that degree of cold at which it 
 begins to be condensed, and opposite to it in the table 
 above mentioned, will be found the force of vapour. 
 From the various facts mentioned in the essay it is obvious, 
 that vapour contracts no chemical union with any of the 
 gases in the atmosphere ; this fact has since been enforced 
 in the Annales de Chimie, vol. xlii. by Clement and 
 Desorme. 
 
 M. De Saussure found by an excellent experiment, 
 that dry air of 64 will admit so much vapour as to 
 increase its elasticity, T \. This I have repeated nearly 
 in his manner, and found a similar result. But the table 
 he has given us of aqueous vapour at other temperatures 
 is very far wrong, especially at temperatures distant from 
 64. The numbers were not the result of direct experi- 
 ment, like the one above. If we could obtain the 
 temperatures of all parts of the earth's surface, for any 
 given time, a mean of them would probably be 57 or 
 58. Now if we may suppose the force of vapour 
 equivalent to that of 55, at a medium, it will, from the 
 table, be equal to .443 of mercury ; or, nearly T ^ of the 
 whole atmosphere. This it will be perceived is calculated 
 to be the weight of vapour in the whole atmosphere of 
 the earth. If that incumbent over any place at any time 
 be required, it may be found as directed above. 
 
 3. Of the Weight of the Carbonic Acid Atmosphere. 
 
 From some observations of Humboldt, I was led to 
 expect about yj^ part of the weight of the atmosphere to 
 be carbonic acid gas : but I soon found that the propor- 
 tion was immensely overrated. From repeated experi- 
 ments, all nearly agreeing in their results, and made 
 at different seasons of the year, I have found, that if 
 a glass vessel filled with 102,400 grains of rain water 
 
12 Dalton. 
 
 be emptied in the open air, and 125 grains of strong lime 
 water be poured in, and the mouth then closed; by 
 sufficient time and agitation, the whole of the lime water 
 is just saturated by the acid gas it finds in that volume of 
 air. But 125 grains of the lime water used require 70 
 grain measures of carbonic acid gas to saturate it ; there- 
 fore, the 102,400 grain measures of common air contain 
 70 of carbonic acid ; or yj 1 ^ of the whole. The weight 
 of the carbonic acid atmosphere then is to that of the 
 whole compound as i : 1460 ; but the weight of carbonic 
 acid gas in a given portion of air at the earth's surface, is 
 nearly y^ 1 ^ of the whole ; because the specific gravity of 
 the gas is \\ that of common air. I have since found 
 that the air in an assembly, in which two hundred people 
 had breathed for two hours, with the windows and doors 
 shut, contained little more than i per cent, of carbonic 
 acid gas. 
 
 Having now determined the force with which each 
 atmosphere presses on the earth's surface, or in other 
 words, its weight ; it remains next to enquire into their 
 specific gravities. 
 
 These may be seen in the following Table. 
 
 Atmospheric air, - i.ooo 
 
 Azotic gas, .966 
 
 Oxygenous gas, 1.127 
 
 Carbonic acid gas, - 1.50 
 
 Aqueous vapour, - .700 
 
 Hydrogenous gas, - .077* 
 
 Kirwan and Lavoisier are my authorities for these 
 numbers; except oxygenous gas and aqueous vapour. 
 
 * The specific gravity of hydrogen must be rated too low : if 100 
 oxygen require 185 hydrogen by measure, according to this 89 
 oxygen would require only 1 1 hydrogen to form water ; whereas 85 
 require 15. Hydrogen ought to be found about T ^ part of the weight 
 of common air. 
 
Proportion of Gases in the Atmosphere. 13 
 
 For the former I am indebted to Mr Davy's Chemical 
 Researches ; his number is something greater than theirs : 
 I prefer it, because, being determined with at least equal 
 attention to accuracy with the others, it has this further 
 claim for credit, that 21 parts of gas of this specific 
 gravity, mixed with 79 parts of azotic gas, make a com- 
 pound of exactly the same specific gravity as the 
 atmosphere, as they evidently ought to do, setting aside 
 the unfounded notion of their forming a chemical com- 
 pound. The specific gravity of aqueous vapour I have 
 determined myself both by analytic and synthetic methods, 
 after the manner of De Saussure : that is, by abstracting 
 aqueous vapour of a known force from a given quantity 
 of air, and weighing the water obtained and admitting 
 a given weight of water to dry air and comparing the loss 
 with the increased elasticity. De Saussure makes the 
 specific gravity to be ,71 or ,75 ; but he used caustic 
 alkali as the absorbent, which would extract the carbonic 
 acid as well as the aqueous vapour from the air. From 
 the experiments of Pictet and Watt, I deduce the specific 
 gravity of aqueous vapour to be ,61 and ,67 respectively. 
 Upon the whole, therefore, it is probable that ,7 is very 
 nearly accurate. 
 
 We have now sufficient data to form tables answering 
 to the two first objects of our enquiry. 
 
 I. Table of the Weights of the different Gases constituting 
 the Atmosphere. 
 
 Inch of Mercury. 
 
 Azotic gas 23.36 
 
 Oxygenous gas - 6.18 
 
 Aqueous vapour -44 
 
 Carbonic acid gas .02 
 
 30.00 
 
14 Dalton. 
 
 II. Table of the proportional Weights of the different Gases 
 in a given volume of Atmospheric Air, taken at the 
 Surface of the Earth. 
 
 Per Cent. 
 
 Azotic gas 75.55 
 
 Oxygenous gas - 23.32 
 
 Aqueous vapour 1.03* 
 
 Carbonic acid gas - .10 
 
 100.00 
 
 III. On the Proportion of Gases at different Elevations. 
 
 M. Berthollet seems to think that the lower strata of 
 the atmosphere ought to contain more oxygen than the 
 upper, because of the greater specific gravity of oxygenous 
 gas, and the slight affinity of the two gases for each other. 
 (See Annal. de Chimie, Tom. 34. page 85.) As I am 
 unable to conceive even the possibility of two gases being 
 held together by affinity, unless their particles unite so as 
 to form one centre of repulsion out of two or more (in 
 which case they become one gas) I cannot see why 
 rarefaction should either decrease or increase this 
 supposed affinity. I have little doubt, however, as to the 
 fact of oxygenous gas observing a diminishing ratio in 
 ascending ; for, the atmospheres being independent on 
 each other, their densities at different heights must be 
 regulated by their specific gravities. Hence, if we take the 
 azotic atmosphere as a standard, the oxygenous and the 
 carbonic acid will observe a decreasing ratio to it in 
 ascending, and the aqueous vapour an increasing one. 
 The specific gravity of oxygenous and azotic gases being 
 as 7 to 6 nearly, their diminution in density will be the 
 same at heights reciprocally as their specific gravities. 
 
 * The proportion of aqueous vapour must be understood to be 
 variable for any one place : the others are permanent or nearly so. 
 
Absorption of Gases by Water, &c. 15 
 
 Hence it would be found, that at the height of Mount 
 Blanc (nearly three English miles) the ratio of oxygenous 
 gas to azotic in a given volume of air, would be nearly as 
 20 to 80 ; consequently it follows that at any ordinary 
 heights the difference in the proportions will be scarcely 
 if at all perceptible. * 
 
 ON THE ABSORPTION OF GASES BY 
 WATER AND OTHER LIQUIDS. BY 
 JOHN DALTON.f 
 
 Read Oct. 21, 1803. 
 
 i. T F a quantity of pure water be boiled rapidly for a 
 1 short time in a vessel with a narrow aperture, or 
 if it be subjected to the air-pump, the air exhausted from 
 the receiver containing the water, and then be briskly 
 agitated for some time, very nearly tbj.e whole of any- gas. 
 the water may contain, will be extricated from it. 
 
 2. If a quantity of water thus freed from air be agitated 
 in any kind of gas, not chemically uniting with water, it 
 will absorb its bulk of the gas, or otherwise a part of it 
 equal to some one of the following fractions, namely, |, 
 
 T7> FI> -ifs* &c - these bein & the cubes f the reciprocals 
 of the natural numbers i, 2, 3, &c. or - 3 , - 3 , - 3 , - 3 , &c. 
 
 the same gas always being absorbed in the same propor- 
 
 * Air brought from the summit of Helvelyn, in Cumberland (noo 
 yards above the sea Barometer being 26.60) in July 1804, gave no 
 perceptible differences from the air taken in Manchester. M. Gay- 
 Lussac determines the constitution of air brought from an elevation 
 of four miles to be the same as that at the earth's surface. 
 
 t From the Memoirs of the Literary and Philosophical Society 
 of Manchester, Second Series, Volume I., 1805, pp. 271-287. The 
 table appended to this paper is Dalton's first table of atomic weights. 
 
i6 
 
 Dalton. 
 
 tion, as exhibited in the following table : It must be 
 understood that the quantity of gas is to be measured at 
 the pressure and temperature with which the impregnation 
 is effected. 
 
 Bulk absorbed, the bulk 
 of water being unity. 
 
 ?-' 
 
 Carbonic acid gas, sul- 
 phuretted hydrogen, nitrous 
 oxide.* 
 
 i _ i 
 
 ?~* 
 
 Olefiant gas, of the Dutch 
 chemists. 
 
 i _ i 
 
 ?~^ 
 
 Oxygenous gas, nitrous 
 gas,f carburetted hydrogen 
 gas, from stagnant water. 
 
 i _ i 
 
 ?-* 
 
 Azotic gas, hydrogenous 
 gas, carbonic oxide. 
 
 i_i 
 
 ~3~T2T 
 
 None discovered. 
 
 3. The gas thus absorbed may be recovered from the 
 
 * According to Mr William Henry's experiments, water does not 
 imbibe quite its bulk of nitrous oxide ; in one or two instances with 
 me it has come very near it : The apparent deviation of this gas, 
 may be owing to the difficulty of ascertaining the exact degree of 
 its impurity. 
 
 t About -fa of nitrous gas is usually absorbed ; and ^ T is recover- 
 able : This difference is owing to the residuum of oxygen in the 
 water, each measure of which takes 3^ of nitrous gas to saturate it, 
 when in water. Perhaps it may be found that nitrous gas usually 
 contains a small portion of nitrous oxide. 
 
Absorption of Gases by Water, &c. 17 
 
 water the same in quantity and quality as it entered, by 
 the means pointed out in the ist article. 
 
 4. If a quantity of water free from air be agitated with 
 a mixture of two or more gases (such as atmospheric air) 
 the water will absorb portions of each gas the same as if 
 they were presented to it separately in their proper 
 density. 
 
 Ex. gr. Atmospheric air, consisting of 79 parts azotic 
 gas, and 21 parts oxygenous gas, per cent. 
 
 Water absorbs T T of T 7 ^j-, azotic gas= 1.234 
 2T o f TTO oxygen gas = .778 
 
 Sum, per cent. 2.012 
 
 5. If water impregnated with any one gas (as hydro- 
 genous) be agitated with another gas equally absorbable 
 (as azotic) there will apparently be no absorption of the 
 latter gas ; just as much gas being found after agitation 
 as was introduced to the water; but upon examination 
 the residuary gas will be found a mixture of the two, and 
 the parts of each, in the water, will be exactly propor- 
 tional to those out of the water. 
 
 6. If water impregnated with any one gas be agitated 
 with another gas less or more absorbable ; there will 
 apparently be an increase or diminution of the latter; 
 but upon examination the residuary gas will be found a 
 mixture of the two, and the proportions agreeable to 
 article 4. 
 
 7. If a quantity of water in a phial having a ground 
 stopper very accurately adapted, be agitated with any gas, 
 or mixture of gases, till the due share has entered the 
 water ; then, if the stopper be secured, the phial may be 
 exposed to any variation of temperature^ without disturb- 
 ing the equilibrium : That is, the quantity of gas in the 
 water will remain the same whether it be exposed to heat 
 or cold, if the stopper be air-tight. 
 
 B 
 
1 8 Dalton. 
 
 N.B. The phial ought not to be near full of water, and 
 the temperature should be between 32 and 212. 
 
 8. If water be impregnated with one gas (as oxygenous), 
 and another gas, having an affinity for the former (as 
 nitrous), be agitated along with it ; the absorption of the 
 latter gas will be greater, by the quantity necessary to 
 saturate the former, than it would have been if the water 
 had been free from gas.* 
 
 9. Most liquids free from viscidity, such as acids, 
 alcohol, liquid sulphurets, and saline solutions in water, 
 absorb the same quantity of gases as pure water ; except 
 they have an affinity for the gas, such as the sulphurets 
 for oxygen, &c. 
 
 The preceding articles contain the principal facts neces- 
 sary to establish the theory of absorption : Those that 
 follow are of a subordinate nature, and partly deducible 
 as corollaries to them. 
 
 10. Pure distilled water, rain and spring water usually 
 contain nearly their due share of atmospheric air : if not, 
 they quickly acquire that share by agitation in it, and 
 lose any other gas they may be impregnated with. It is 
 remarkable however that water by stagnation, in certain 
 circumstances, loses part or all of its oxygen, notwithstand- 
 ing its constant exposition to the atmosphere. This I 
 have uniformly found to be the case in my large wooden 
 pneumatic trough, containing about 8 gallons, or i^ cubic 
 foot of water. Whenever this is replenished with toler- 
 ably pure rain water, it contains its share of atmospheric 
 
 * One part of oxygenous gas requires 3.4 of nitrous gas to saturate 
 it in water. It is agreeable to this that the rapid mixture of oxy- 
 genous and nitrous gas over a broad surface of water, occasions a 
 greater diminution than otherwise. In fact, the nitrous acid is 
 formed this way ; whereas, when water is not present, the nitric 
 acid is formed, which requires just half the quantity of nitrous gas, 
 as I have lately ascertained. 
 
Absorption of Gases by Water , &c. 19 
 
 air ; but in process of time it becomes deficient of oxygen : 
 In three months the whole surface has been covered with 
 a pellicle, and no oxygenous gas whatever was found in 
 the water. It was grown offensive, but not extremely so ; 
 it had not been contaminated with any material portion 
 of metallic or sulphureous mixtures, or any other article 
 to which the effect could be ascribed.'* The quantity of 
 azotic gas is not materially diminished by stagnation, if 
 at all. These circumstances, not being duly noticed, have 
 been the source of great diversity in the results of differ- 
 ent philosophers upon the quantity and quality of atmo- 
 spheric air in water. By article 4, it appears that 
 atmospheric air expelled from water ought to have 38 per 
 cent, oxygen ; whereas by this article air may be expelled 
 from water that shall contain from 38 to o per cent, of 
 oxygen. The disappearance of oxygenous gas in water, 
 I presume, must be owing to some impurities in the water 
 which combine with the oxygen. Pure rain water that 
 had stood more than a year in an earthenware bottle had 
 lost none of its oxygen. 
 
 11. If water free from air be agitated with a small 
 portion of atmospheric air (as -^ of its bulk) the residuum 
 of such air will have proportionally less oxygen than the 
 original : If we take ^, as above, then the residuum will 
 have only 1 7 per cent, oxygen ; agreeably to the prin- 
 ciple established in article 4. This circumstance accounts 
 for the observations made by Dr Priestley, and Mr 
 William Henry, that water absorbs oxygen in preference 
 to azot. 
 
 12. If a tall glass vessel containing a small portion of 
 gas be inverted into a deep trough of water and the gas 
 thus confined by the glass, and the water be briskly 
 agkated, it will gradually disappear. 
 
 * It was drawn from a leaden cistern. 
 
22 Dalton. 
 
 residuary gas was ^ pure, then it was inferred that water 
 would take its bulk of that gas. The principle was the 
 same in using the phial ; only a small quantity of the gas 
 was admitted, and the agitation was longer. 
 
 There are two very important facts contained in the 
 second article. The first is, that the quantity of gas 
 absorbed is as the density or pressure. This was dis- 
 covered by Mr Wm. Henry, before either he or I had 
 formed any theory on the subject. 
 
 The other is that the density of the gas in the water has 
 a special relation to that out of the water, the distance of 
 the particles within being always some multiple of that 
 without : Thus, in the case of carbonic acid, &c. the dis- 
 tance within and without is the same, or the gas within 
 the water is of the same density as without ; in defiant 
 gas the distance of the particles in the water is twice that 
 without ; in oxygenous gas, &c. the distance is just three 
 times as great within as without ; and in azotic, &c. it is 
 four times. This fact was the result of my own enquiry. 
 The former of these, I think, decides the effect to be 
 mechanical ; and the latter seems to point to the principle 
 on which the equilibrium is adjusted. 
 
 The facts noticed in the 4th, 5th and 6th articles, were 
 investigated a priori from the mechanical hypothesis, and 
 the notion of the distinct agency of elastic fluids when 
 mixed together. The results were found entirely to agree 
 with both, or as nearly as could be expected from experi- 
 ments of such nature. 
 
 The facts mentioned in the yth article, are of great im- 
 portance in a theoretic view ; for, if the quantity of gas 
 absorbed depend upon mechanical principles, it cannot 
 be affected by temperature in confined air, as the 
 mechanical effect of the external and internal air are alike 
 increased by heat, and the density not at all affected in 
 those circumstances. I have tried the experiments in a 
 
Absorption of Gases by Water, &c. 23 
 
 considerable variety of temperature without perceiving 
 any deviation from the principle. It deserves further 
 attention. 
 
 If water be, as pointed out by this essay, a mere 
 receptacle of gases, it cannot affect their affinities : hence 
 what is observed in the 8th article is too obvious to need 
 explanation. And if we find the absorption of gases to 
 arise not from a chemical but a mechanical cause, it may be 
 expected that all liquids having an equal fluidity with 
 water, will absorb like portions of gas. In several liquids 
 I have tried no perceptible difference has been found ; 
 but this deserves further investigation. 
 
 After what has been observed, it seems unnecessary to 
 add any explanation of the loth and following articles. 
 
 Theory of the Absorption of Gases by Water, &c. 
 
 From the facts developed in the preceding articles, the 
 following theory of the absorption of gases by water seems 
 deducible. 
 
 1. All gases that enter into water and other liquids by 
 means of pressure, and are wholly disengaged again by 
 the removal of that pressure, are mechanically mixed with 
 the liquid, and not chemically combined with it. 
 
 2. Gases so mixed with water, &c. retain their elas- 
 ticity or repulsive power amongst their own particles, just 
 the same in the water as out of it, the intervening water 
 having no other influence in this respect than a mere 
 vacuum. 
 
 3. Each gas is retained in water by the pressure of gas 
 of its own kind incumbent on its surface abstractedly con- 
 sidered, no other gas with which it may be mixed having 
 any permanent influence in this respect. 
 
 4. When water has absorbed its bulk of carbonic acid 
 gas, &c., the gas does not press on the water at all, but 
 presses on the containing vessel just as if no water were 
 
24 Dalton. 
 
 in. When water has absorbed its proper quantity of 
 oxygenous gas, &c. that is, -^ of its bulk, the exterior 
 gas presses on the surface of the water with f f of its force, 
 and on the internal gas with ^ T of its force, which force 
 presses upon the containing vessel and not on the water. 
 With azotic and hydrogenous gas the proportions are ff 
 and 3^ respectively. When water contains no gas, its 
 surface must support the whole pressure of any gas 
 admitted to it, till the gas has, in part, forced its way into 
 the water. 
 
 5. A particle of gas pressing on the surface of water is 
 analogous to a single shot pressing upon the summit of a 
 square pile of them. As the shot distributes its pressure 
 equally amongst all the individuals forming the lowest 
 stratum of the pile, so the particle of gas distributes its 
 pressure equally amongst every successive horizontal 
 stratum of particles of water downwards till it reaches the 
 sphere of influence of another particle of gas. For in- 
 stance ; let any gas press with a given force on the surface 
 of water, and let the distance of the particles of gas from 
 each other be to those of water as i o to i ; then each 
 particle of gas must divide its force equally amongst 100 
 particles of water, as follows : It exerts its immediate 
 force upon 4 particles of water ; those 4 press upon 9, the 
 9 upon 1 6, and so on according to the order of square 
 numbers, till 100 particles of water have the force distri- 
 buted amongst them ; and in the same stratum each 
 square of 100, having its incumbent particle of gas, the 
 water below this stratum is uniformly pressed by the gas, 
 and consequently has not its equilibrium disturbed by 
 that pressure. 
 
 6. When water has absorbed ^ T of its bulk of any gas, 
 the stratum of gas on the surface of the water presses with 
 7- of its force on the water, in the manner pointed out in 
 the last article, and with ^ T of its force on the uppermost 
 
Absorption of Gases by Water, &c. 25 
 
 stratum of gas in the water : The distance of the two 
 strata of gas must be nearly 2 7 times the distance of the 
 particles in the incumbent atmosphere and 9 times the 
 distance of the particles in the water. This compara- 
 tively great distance of the inner and outer atmosphere 
 arises from the great repulsive power of the latter, on 
 account of its superior density, or its presenting 9 particles 
 of surface to the other i . When / T is absorbed the dis- 
 tance of the atmospheres becomes 64 times the distance 
 of two particles in the outer, or 16 times that of the 
 inner. 
 
 7. An equilibrium between the outer and inner atmo- 
 spheres can be established in no other circumstance than 
 that of the distance of the particles of one atmosphere 
 being the same or some multiple of that of the other ; and 
 it is probable the multiple cannot be more than 4. For 
 in this case the distance of the inner and outer atmo- 
 spheres is such as to make the perpendicular force of each 
 particle of the former on those particles of the latter that 
 are immediately subject to its influence, physically speak- 
 ing, equal ; and the same may be observed of the small 
 lateral force. 
 
 8. The greatest difficulty attending the mechanical 
 hypothesis, arises from different gases observing differ- 
 ent laws. Why does water not admit its bulk of every 
 kind of gas alike? This question I have duly con- 
 sidered, and though I am not yet able to satisfy 
 myself completely, I am nearly persuaded that the cir- 
 cumstance depends upon the weight and number of the 
 ultimate particles of the several gases : those whose par- 
 ticles are lightest and single being least absorbable, and 
 the others more according as they increase in weight and 
 complexity.* An inquiry into the relative weights of the 
 
 * Subsequent experience renders this conjecture less probable. 
 
26 Dalton. 
 
 ultimate particles of bodies is a subject, as far as I know, 
 entirely new : I have lately been prosecuting this enquiry 
 with remarkable success. The principle cannot be entered 
 upon in this paper ; but I shall just subjoin the results, as 
 far as they appear to be ascertained by my experiments. 
 
 Table of the relative weights of the ultimate particles of 
 
 gaseous and other bodies, 
 
 Hydrogen - i 
 
 Azot - 4.2 
 
 Carbone - 4.3 
 
 Ammonia - - 5.2 
 
 Oxygen - 5.5 
 
 Water - - 6.5 
 
 Phosphorus - 7.2 
 
 Phosphuretted hydrogen - 8.2 
 
 Nitrous gas - - 9-3 
 
 Ether - 9.6 
 
 Gaseous oxide of carbone - - 9.8 
 
 Nitrous oxide - 13.7 
 
 Sulphur 14.4 
 
 Nitric acid - 15.2 
 
 Sulphuretted hydrogen - - 15.4 
 
 Carbonic acid - 15.3 
 
 Alcohol - 15.1 
 
 Sulphureous acid - - 19.9 
 
 Sulphuric acid 25.4 
 
 Carburetted hydrogen from stag, water - 6.3 
 
 Olefiant gas - 5-3 
 
/ 
 
 Constitution of Bodies. 27 
 
 ON THE CONSTITUTION OF BODIES. 
 BY JOHN DALTON* 
 
 THERE are three distinctions in the kinds of bodies, 
 or three states, which have more especially claimed 
 the attention of philosophical chemists ; namely, those 
 which are marked by the terms elastic fluids, liquids, and 
 solids. A very familiar instance is exhibited to us in water, 
 of a body, which, in certain circumstances, is capable of 
 assuming all the three states. In steam we recognise a 
 perfectly elastic fluid, in water a perfect liquid, and in ice 
 a complete solid. These observations have tacitly led to 
 the conclusion which seems universally adopted, that all 
 bodies of sensible magnitude, whether liquid or solid, are 
 constituted of a vast number of extremely small particles, 
 or atoms of matter bound together by a force of attrac- 
 tion, which is more or less powerful according to circum- 
 stances, and which as it endeavours to prevent their 
 separation, is very properly called in that view, attraction 
 of cohesion ; but as it collects them from a dispersed state 
 (as from steam into water) it is called, attraction of aggre- 
 gation, or more simply, affinity. Whatever names it may 
 go by, they still signify one and the same power. It is 
 not my design to call in question this conclusion, which 
 appears completely satisfactory; but to show that we 
 have hitherto made no use of it, and that the consequence 
 of the neglect, has been a very obscure view of chemical 
 agency, which is daily growing more so in proportion to 
 the new lights attempted to be thrown upon it. 
 
 The opinions I more particularly allude to, are those 
 of Berthollet on the Laws of chemical affinity ; such as 
 that chemical agency is proportional to the mass, and 
 that in all chemical unions, there exist insensible grada- 
 
 * From A New System of Chemical Philosophy, Manchester 
 1808, pp. 141-143. 
 
28 Dalton. 
 
 tions in the proportions of the constituent principles. 
 The inconsistence of these opinions, both with reason 
 and observation, cannot, I think, fail to strike every one 
 who takes a proper view of the phenomena. 
 
 Whether the ultimate particles of a body, such as water, 
 are all alike, that is, of the same figure, weight, &c. is a 
 question of some importance. From what is known, we 
 have no reason to apprehend a diversity in these par- 
 ticulars : if it does exist in water, it must equally exist in 
 the elements constituting water, namely, hydrogen and 
 oxygen. Now it is scarcely possible to conceive how the 
 aggregates of dissimilar particles should be so uniformly 
 the same. If some of the particles of water were heavier 
 than others, if a parcel of the liquid on any occasion 
 were constituted principally of these heavier particles, it 
 must be supposed to affect the specific gravity of the 
 mass, a circumstance not known. Similar observations 
 may be made on other substances. Therefore we may 
 conclude that the ultimate particles of all homogeneous 
 bodies are perfectly alike in weight, figure, &c. In other 
 words, &*y|particle of water is like every other particle 
 of water ; every particle of hydrogen is like every other 
 particle of hydrogen, &c. 
 
 ON CHEMICAL SYNTHESIS. 
 BY JOHN DALTON.* 
 
 WHEN any body exists in the elastic state, its 
 ultimate particles are separated from each other 
 to a much greater distance than in any other state ; each 
 particle occupies the centre of a comparatively large 
 sphere, and supports its dignity by keeping all the rest, 
 
 * From A New System of Chemical Philosophy, Manchester 
 1808, pp. 211-216 and 219-220. 
 
Chemical Synthesis. 29 
 
 which by their gravity, or otherwise are disposed to 
 encroach upon it, at a respectful distance. When we 
 attempt to conceive the number of particles in an atmo- 
 sphere, it is somewhat like attempting to conceive the 
 number of stars in the universe ; we are confounded with 
 the thought. But if we limit the subject, by taking a 
 given volume of any gas, we seem persuaded that, let the 
 divisions be ever so minute, the number of particles must 
 be finite ; just as in a given space of the universe, the 
 number of stars and planets cannot be infinite. 
 
 Chemical analysis and synthesis go no farther than to the 
 separation of particles one from another, and to their re- 
 union. No new creation or destruction of matter is within 
 the reach qf chemical agency. We might as well attempt to 
 introduce a new planet into the solar system, or to annihil- 
 ate one already in existence, as to create or destroy a particle 
 of hydrogen. All the changes we can produce, consist in 
 separating particles that are in a state of cohesion or combin- 
 ation, and joining those that were previously at a distance. 
 
 In all chemical investigations, it has justly been con- 
 sidered an important object to ascertain the relative 
 weights of the simples which constitute a compound. 
 But unfortunately the enquiry has terminated here; 
 whereas from the relative weights in the mass, the relative 
 weights of the ultimate particles or atoms of the bodies 
 might have been inferred, from which their number and 
 weight in various other compounds would appear, in 
 order to assist and to guide future investigations, and to 
 correct their results. Now it is one great object of this 
 work, to show the importance and advantage of ascertain- 
 ing the relative weights of the ultimate particles ; both of 
 simple and compound bodies, the number of simple element- 
 ary particles ivhich constitute one compound particle, and 
 the number of less compound particles which enter into the 
 formation of one more compound particle. 
 
30 Da/ton. 
 
 If there are two bodies, A and B, which are disposed 
 to combine, the following is the order in which the com- 
 binations may take place, beginning with the most 
 simple : namely, 
 
 I atom of A + I atom of B = atom of C, binary. 
 
 1 atom of A + 2 atoms of B = atom of D, ternary. 
 
 2 atoms of A + I atom of B = atom of E, ternary. 
 
 I atom of A + 3 atoms of B = atom of F, quaternary. 
 
 3 atoms of A + I atom of B = atom of G, quaternary. 
 
 &c. &c. 
 
 The following general rules may be adopted as guides 
 in all our investigations respecting chemical synthesis. 
 
 ist. When only one combination of two bodies can be 
 obtained, it must be presumed to be a binary one, unless 
 some cause appear to the contrary. 
 
 2d. When two combinations are observed,' they must 
 be presumed to be a binary and a ternary. 
 
 3d. When three combinations are obtained, we may 
 expect one to be a binary, and the other two ternary. 
 
 4th. When four combinations are observed, we should 
 expect one binary, two ternary, and one quaternary, &c. 
 
 5th. A binary compound should always be specifically 
 heavier than the mere mixture of its two ingredients. 
 
 6th. A ternary compound should be specifically heavier 
 than the mixture of a binary and a simple, which would, 
 if combined, constitute it ; c. 
 
 yth. The above rules and observations equally apply, 
 when two bodies, such as C and D, D and E, &c. are 
 combined. 
 
 From the application of these rules, to the chemical 
 facts already well ascertained, we deduce the following 
 conclusions ; ist. That water is a binary compound of 
 hydrogen and oxygen, and the relative weights of the two 
 elementary atoms are as i : 7, nearly ; 2d. That ammonia 
 is a binary compound of hydrogen and azote, and the 
 relative weights of the two atoms are as 1:5, nearly ; 3d. 
 That nitrous gas is a binary compound of azote and 
 
Chemical Synthesis. 31 
 
 oxygen, the atoms of which weigh 5 and 7 respectively ; 
 that nitric acid is a binary or ternary compound accord- 
 ing as it is derived, and consists of one atom of azote 
 and two of oxygen, together weighing 1 9 ; that nitrous 
 oxide is a compound similar to nitric acid, and consists 
 of one atom of oxygen and two of azote, weighing 17 ; 
 that nitrous acid is a binary compound of nitric acid and 
 nitrous gas, weighing 31 ; that oxynitric acid is a binary 
 compound of nitric acid and oxygen, weighing 26 ; 4th. 
 That carbonic oxide is a binary compound, consisting of 
 one atom of charcoal, and one of oxygen, together weigh- 
 ing nearly 1 2 ; that carbonic acid is a ternary compound 
 (but sometimes binary) consisting of one atom of char- 
 coal, and two of oxygen, weighing 1 9 ; &c. &c. In all 
 these cases the weights are expressed in atoms of hydrogen, 
 each of which is denoted by unity. 
 
 In the sequel, the facts and experiments from which 
 these conclusions are derived, will be detailed ; as well as 
 a great variety of others from which are inferred the con- 
 stitution and weight of the ultimate particles of the prin- 
 cipal acids, the alkalis, the earths, the metals, the metallic 
 oxides and sulphurets, the long train of neutral salts, and 
 in short, all the chemical compounds which have hitherto 
 obtained a tolerably good analysis. Several of the con- 
 clusions will be supported by original experiments. 
 
 From the novelty as well as importance of the ideas 
 suggested in this chapter, it is deemed expedient to give 
 plates, exhibiting the mode of combination in some of 
 the more simple cases. A specimen of these accompanies 
 this first part. The elements or atoms of such bodies as 
 are conceived at present to be simple, are denoted by a 
 small circle, with some distinctive mark ; and the com- 
 binations consist in the juxta-position of two or more of 
 these ; when three or more particles of elastic fluids are 
 combined together in one, it is to be supposed that the 
 
Dalton. 
 
 particles of the same kind repel each other, and therefore 
 take their stations accordingly. 
 
 ELEMENTS . 
 045 
 
 O <D O G 
 
 9 l u 19 u 
 
 18 19 90, 
 
 OO GO (DO 
 
 ft 
 
 O 
 
 
 
 
 GOO) OCDO OO 
 
 Qua&rnwry 
 
 Jl 
 
 35 
 
 37 
 
Chemical SyntJiesis. 33 
 
 This plate contains the arbitrary marks or signs chosen to repre- 
 sent the several chemical elements or ultimate particles. 
 Fig. 
 
 1 Hydrog. its rel. weight I 
 
 2 Azote, 5 
 
 3 Carbone or charcoal, - 5 
 
 4 Oxygen, - - - 7 
 
 5 Phosphorus, 9 
 
 6 Sulphur, - - -13 
 
 7 Magnesia, - - -20 
 
 8 Lime, - - - - 23 
 
 9 Soda, - - - - 28 
 10 Potash, - - - 42 
 
 Fig. 
 
 11 Strontites, - - - 46 
 
 12 Barytes, - 68 
 
 13 Iron, - - - -38 
 
 14 Zinc, - - - - 56 
 
 15 Copper, - 56 
 
 16 Lead, - - - - 95 
 
 17 Silver, - 100 
 
 18 Platina, - - - 100 
 
 19 Gold, - --- 140 
 
 20 Mercury, - - - 167 
 
 21. An atom of water or steam, composed of I of oxygen and 
 
 I of hydrogen, retained in physical contact by a strong 
 affinity, and supposed to be surrounded by a common 
 atmosphere of heat ; its relative weight = - -8 
 
 22. An atom of ammonia, composed of I of azote and I of 
 
 hydrogen - 6 
 
 23. An atom of nitrous gas, composed of I of azote and I of 
 
 oxygen 12 
 
 24. An atom of olefiant gas, composed of I of carbone and I of 
 
 hydrogen 6 
 
 25. An atom of carbonic oxide composed of I of carbone and I 
 
 of oxygen 12 
 
 26. An atom of nitrous oxide, 2 azote + I oxygen - - -17 
 
 27. An atom of nitric acid, I azote + 2 oxygen - - - 19 
 
 28. An atom of carbonic acid, I carbone + 2 oxygen - - 19 
 
 29. An atom of carburetted hydrogen, I carbone + 2 hydrogen 7 
 
 30. An atom of oxynitric acid, I azote + 3 oxygen - - 26 
 
 31. An atom of sulphuric acid, I sulphur + 3 oxygen - - 34 
 
 32. An atom of sulphuretted hydrogen, I sulphur + 3 hy- 
 
 drogen 16 
 
 33. An atom of alcohol, 3 carbone + I hydrogen - - - 16 
 
 34. An atom of nitrous acid, I nitric acid + I nitrous gas - 31 
 
 35. An atom of acetous acid, 2 carbone + 2 water - - 26 
 
 36. An atom of nitrate of ammonia, I nitric acid + I ammonia 
 
 + i water 33 
 
 37. An atom of sugar, i alcohol + I carbonic acid - - 35 
 
 Enough has been given to show the method ; it will be quite un- 
 necessary to devise characters and combinations of them to exhibit 
 to view in this way all the subjects that come under investigation ; 
 nor is it necessary to insist upon the accuracy of all these compounds, 
 
 C 
 
34 Wollaston. 
 
 both in number and weight ; the principle will be entered into more 
 particularly hereafter, as far as respects the individual results. It is 
 not to be understood that all those articles marked as simple sub- 
 stances, are necessarily such by the theory ; they are only necessarily 
 of such weights. Soda and potash, such as they are found in com- 
 bination with acids, are 28 and 42 respectively in weight ; but 
 according to Mr Davy's very important discoveries, they are metallic 
 oxides ; the former then must be considered as composed of an atom 
 of metal, 21, and one of oxygen, 7 ; and the latter, of an atom of 
 metal, 35, and one of oxygen, 7. Or, soda contains 75 per cent, 
 metal and 25 oxygen ; potash, 83.3 metal and 16.7 oxygen. It is 
 particularly remarkable, that according to the above-mentioned 
 gentleman's essay on the Decomposition and Composition of the 
 fixed alkalies, in the Philosophical Transactions (a copy of which 
 essay he has just favoured me with) it appears that " the largest 
 quantity of oxygen indicated by these experiments was for potash 
 17, and for soda, 26 parts in 100, and the smallest 13 and 19." 
 
 ON SUPER-ACID AND SUB-ACID SALTS. 
 BY WILLIAM HYDE WOLLASTON, 
 M.D., Sec. R.S.* 
 
 Read Jan. 28, 1808. 
 
 IN the paper which has just been read to the Society, 
 Dr Thomson has remarked, that oxalic acid unites 
 to strontian as well as to potash in two different propor- 
 tions, and that the quantity of acid combined with each 
 of these bases in their super-oxalates, is just double of 
 that which is saturated by the same quantity of base in 
 their neutral compounds.! 
 
 As I had observed the same law to prevail in various 
 other instances of super-acid and sub-acid salts, I thought 
 
 * From the Philosophical Transactions, vol. 98 (for 1808), pp. 
 96-102. 
 
 t [See the extracts from Dr Thomson's paper on Oxalic Acid, on 
 page 41.] 
 

 Super-acid and Sub-acid Salts. 35 
 
 it not unlikely that this law might obtain generally in such 
 compounds, and it was my design to have pursued the 
 subject with the hope of discovering the cause to which 
 so regular a relation might be ascribed. 
 
 But since the publication of Mr Dalton's theory of 
 chemical combination, as explained and illustrated by Dr 
 Thomson,* the inquiry which I had designed appears to 
 be superfluous, as all the facts that I had observed are but 
 particular instances of the more general observation of 
 Mr Dalton, that in all cases the simple elements of bodies 
 are disposed to unite atom to atom singly, or, if either is 
 in excess, it exceeds by a ratio to be expressed by some 
 simple multiple of the number of its atoms. 
 
 However, since those who are desirous of ascertaining 
 the justness of this observation by experiment, may be 
 deterred by the difficulties that we meet with in attempting 
 to determine with precision the constitution of gaseous 
 bodies, for the explanation of which Mr Dalton's theory 
 was first conceived, and since some persons may imagine 
 that the results of former experiments on such bodies do 
 not accord sufficiently to authorize the adoption of a new 
 hypothesis, it may be worth while to describe a few ex- 
 periments, each of which may be performed with the 
 utmost facility, and each of which affords the most direct 
 proof of the proportional redundance or deficiency of 
 acid in the several salts employed. 
 
 Sub-carbonate of Potash. 
 
 Exp. i. Sub-carbonate of potash recently prepared, is 
 one instance of an alkali having one-half the quantity of 
 acid necessary for its saturation, as may thus be satisfac- 
 torily proved. 
 
 Let two grains of fully saturated and well crystallized 
 carbonate of potash be wrapped in a piece of thin* paper, 
 
 * Thomson's Chemistry, 3d edition, vol. Hi., p. 425. 
 
34 Wollaston. 
 
 both in number and weight ; the principle will be entered into more 
 particularly hereafter, as far as respects the individual results. It is 
 not to be understood that all those articles marked as simple sub- 
 stances, are necessarily such by the theory ; they are only necessarily 
 of such weights. Soda and potash, such as they are found in com- 
 bination with acids, are 28 and 42 respectively in weight ; but 
 according to Mr Davy's very important discoveries, they are metallic 
 oxides ; the former then must be considered as composed of an atom 
 of metal, 21, and one of oxygen, 7 ; and the latter, of an atom of 
 metal, 35, and one of oxygen, 7. Or, soda contains 75 per cent, 
 metal and 25 oxygen ; potash, 83.3 metal and 16.7 oxygen. It is 
 particularly remarkable, that according to the above-mentioned 
 gentleman's essay on the Decomposition and Composition of the 
 fixed alkalies, in the Philosophical Transactions (a copy of which 
 essay he has just favoured me with) it appears that " the largest 
 quantity of oxygen indicated by these experiments was for potash 
 17, and for soda, 26 parts in 100, and the smallest 13 and 19." 
 
 ON SUPER-ACID AND SUB-ACID SALTS. 
 BY WILLIAM HYDE WOLLASTON, 
 M.D., Sec. R.S * 
 
 Read Jan. 28, 1808. 
 
 IN the paper which has just been read to the Society, 
 Dr Thomson has remarked, that oxalic acid unites 
 to strontian as well as to potash in two different propor- 
 tions, and that the quantity of acid combined with each 
 of these bases in their super-oxalates, is just double of 
 that which is saturated by the same quantity of base in 
 their neutral compounds.! 
 
 As I had observed the same law to prevail in various 
 other instances of super-acid and sub-acid salts, I thought 
 
 * From the Philosophical Transactions, vol. 98 (for 1808), pp. 
 96-102. 
 
 t [See the extracts from Dr Thomson's paper on Oxalic Acid, on 
 page 41.] 
 
Super-acid and Sub-acid Salts. 35 
 
 it not unlikely that this law might obtain generally in such 
 compounds, and it was my design to have pursued the 
 subject with the hope of discovering the cause to which 
 so regular a relation might be ascribed. 
 
 But since the publication of Mr Dalton's theory of 
 chemical combination, as explained and illustrated by Dr 
 Thomson,* the inquiry which I had designed appears to 
 be superfluous, as all the facts that I had observed are but 
 particular instances of the more general observation of 
 Mr Dalton, that in all cases the simple elements of bodies 
 are disposed to unite atom to atom singly, or, if either is 
 in excess, it exceeds by a ratio to be expressed by some 
 simple multiple of the number of its atoms. 
 
 However, since those who are desirous of ascertaining 
 the justness of this observation by experiment, may be 
 deterred by the difficulties that we meet with in attempting 
 to determine with precision the constitution of gaseous 
 bodies, for the explanation of which Mr Dalton's theory 
 was first conceived, and since some persons may imagine 
 that the results of former experiments on such bodies do 
 not accord sufficiently to authorize the adoption of a new 
 hypothesis, it may be worth while to describe a few ex- 
 periments, each of which may be performed with the 
 utmost facility, and each of which affords the most direct 
 proof of the proportional redundance or deficiency of 
 acid in the several salts employed. 
 
 Sub-carbonate of Potash. 
 
 Exp. i. Sub-carbonate of potash recently prepared, is 
 one instance of an alkali having one-half the quantity of 
 acid necessary for its saturation, as may thus be satisfac- 
 torily proved. 
 
 Let two grains of fully saturated and well crystallized 
 carbonate of potash be wrapped in a piece of thin'paper, 
 
 * Thomson's Chemistry, 3d edition, vol. iii., p. 425. 
 
36 Wollaston. 
 
 and passed up into an inverted tube filled with mercury, 
 and let the gas be extricated from it by a sufficient quantity 
 of muriatic acid, so that the space it occupies may be 
 marked upon the tube. 
 
 Next, let four grains of the same carbonate be exposed 
 for a short time to a red heat ; and it will be found to 
 have parted with exactly half its gas ; for the gas extri- 
 cated from it in the same apparatus will be found to 
 occupy exactly the same space, as the quantity before 
 obtained from two grains of fully saturated carbonate. 
 
 Sub-carbonate of Soda. 
 
 Exp. 2. A similar experiment may be made with a 
 saturated carbonate of soda, and with the same result ; 
 for this also becomes a true semi-carbonate by being 
 exposed for a short time to a red heat. 
 
 Super-sulphate of Potash. 
 
 By an experiment equally simple, super-sulphate of 
 potash may be shown to contain exactly twice as much 
 acid as is necessary for the mere saturation of the alkali 
 present. 
 
 Exp. 3. Let twenty grains of carbonate of potash 
 (which would be more than neutralized by ten grains of 
 sulphuric acid) be mixed with about twenty-five grains of 
 that acid in a covered crucible of platina, or in a glass 
 tube three quarters of an inch diameter, and five or six 
 inches long. 
 
 By heating this mixture till it ceases to boil, and begins 
 to appear slightly red hot, a part of the redundant acid 
 will be expelled, and there will remain a determinate 
 quantity forming super-sulphate of potash, which when 
 dissolved in water will be very nearly neutralized by an 
 addition of twenty grains more of the same carbonate of 
 potash ; but it is generally found very slightly acid, in 
 
Super -acid and Sub-acid Salts. 37 
 
 consequence of the small quantity of sulphuric acid 
 which remains in the vessel in a gaseous state at a red 
 heat. 
 
 In the preceding experiments, the acids are made to 
 assume a determinate proportion to their base, by heat 
 which cannot destroy them. In those which follow, the 
 proportion which a destructible acid shall assume cannot 
 be regulated by the same means ; but the constitution of 
 its compounds previously formed, may nevertheless be 
 proved with equal facility. 
 
 Super-oxalate of Potash. 
 
 Exp. 4. The common super-oxalate of potash is a salt 
 that contains alkali sufficient to saturate exactly half of 
 the acid present. Hence, if two equal quantities of salt 
 of sorrel be taken, and if one of them be exposed to a red 
 heat, the alkali which remains will be found exactly to 
 saturate the redundant acid of the other portion. 
 
 In addition to the preceding compounds, selected as 
 distinct examples of binacid salts, I have observed one 
 remarkable instance of a more extended and general pre- 
 valence of the law under consideration; for when the 
 circumstances are such as to admit the union of a further 
 quantity of oxalic acid with potash, I found a proportion, 
 though different, yet analogous to the former, regularly to 
 occur. 
 
 Quadroxalate of Potash. 
 
 In attempting to decompose the preceding super-oxalate 
 by means of acids, it appeared that nitric or muriatic 
 acids, are capable of taking only half the alkali, and that 
 the salt which crystallizes after solution in either of these 
 acids, has accordingly exactly four times as much acid as 
 would saturate the alkali that remains. 
 
 Exp. 5. For the purpose of proving that the constitu- 
 
38 Wollaston. 
 
 tion of this compound has been rightly ascertained, the 
 salt thus formed should be purified by a second crystal- 
 lization in distilled water ; after which the alkali of thirty 
 grains must be obtained by exposure to a red heat, in 
 order to neutralize the redundant acid contained in ten 
 grains of the same salt. The quantity of unburned salt 
 contains alkali for one part out of four of the acid present, 
 and it requires the alkali of three equal quantities of the 
 same salt to saturate the three remaining parts of acid. 
 
 The limit to the decomposition of super-oxalate of pot- 
 ash by the above acids, is analogous to that which occurs 
 when sulphate of potash is decomposed by nitric acid ; 
 for in this case also, no quantity of that acid can take more 
 than half the potash, and the remaining salt is converted 
 into a definite super-sulphate, similar to that obtained by 
 heat in the third experiment. 
 
 It is not improbable that many other changes in chem- 
 istry, supposed to be influenced by a general redundance of 
 some one ingredient, may in fact be limited by a new 
 order of affinities taking place at some definite proportion 
 to be expressed by a simple multiple. And though the 
 strong power of crystallizing in oxalic acid, renders the 
 modifications of which its combinations are susceptible 
 more distinct than those of other acids, it seems probable 
 that a similar play of affinities will arise in solution, when 
 other acids exceed their base in the same proportion. 
 
 In order to determine whether oxalic acid is capable of 
 uniting to potash in a proportion intermediate between 
 the double and quadruple quantity of acid, I neutralized 
 forty-eight grains of carbonate of potash with thirty grains 
 of oxalic acid, and added sixty grains more of acid, so 
 that I had two parts of potash of twenty-four grains each, 
 and six equivalent quantities of oxalic acid of fifteen grains 
 each, in solution, ready to crystallize together, if disposed 
 to unite, in the proportion of three to one ; but the first 
 
Super-acid and Sub-acid Salts. 39 
 
 portion of salt that crystallized, was the common bin- 
 oxalate, or salt of sorrel, and a portion selected from the 
 after crystals (which differed very discernibly in their 
 form) was found to contain the quadruple proportion of 
 acid. Hence it is to be presumed, that if these salts 
 could have been perfectly separated, it would have been 
 found, that the two quantities of potash were equally 
 divided, and combined in one instance with two, and in 
 the other with the remaining four out of the six equivalent 
 quantities of acid taken. 
 
 To account for this want of disposition to unite in the 
 proportion of three to one by Mr Dalton's theory, I 
 apprehend he might consider the neutral salt as con- 
 sisting of 
 
 2 particles potash with i acid, 
 The binoxalate 
 
 as i and i, or 2 with 2, 
 
 The quadroxalate 
 
 as i and 2, or 2 with 4, 
 
 in which cases the ratios which I have observed of the 
 acids to each other in these salts would respectively 
 obtain. 
 
 But an explanation, which admits the supposition of a 
 double share of potash in the neutral salt, is not altogether 
 satisfactory ; and I am further inclined to think, that when 
 our views are sufficiently extended, to enable us to reason 
 with precision concerning the proportions of elementary 
 atoms, we shall find the arithmetical relation alone will 
 not be sufficient to explain their mutual action, and that 
 we shall be obliged to acquire a geometrical conception 
 of their relative arrangement in all the three dimensions 
 of solid extension. 
 
 For instance, if we suppose the limit to the approach 
 of particles to be the same in all directions, and hence 
 their virtual extent to be spherical (which is the most 
 
4O Wollaston. 
 
 simple hypothesis); in this case, when different sorts 
 combine singly there is but one mode of union. If they 
 unite in the proportion of two to one, the two particles 
 will naturally arrange themselves at opposite poles of that 
 to which they unite. If there be three, they might be 
 arranged with regularity, at the angles of an equilateral 
 triangle in a great circle surrounding the single spherule ; 
 but in this arrangement, for want of similar matter at the 
 poles of this circle, the equilibrium would be unstable, 
 and would be liable to be deranged by the slightest force 
 of adjacent combinations ; but when the number of one 
 set of particles exceeds in the proportion of four to one, 
 then, on the contrary, a stable equilibrium may again 
 take place, if the four particles are situated at the angles of 
 the four equilateral triangles composing a regular tetra- 
 hedron. 
 
 But as this geometrical arrangement of the primary 
 elements of matter is altogether conjectural, and must 
 rely for its confirmation or rejection upon future inquiry, 
 I am desirous that it should not be confounded with the 
 results of the facts and observations related above, which 
 are sufficiently distinct and satisfactory with respect to the 
 existence of the law of simple multiples. It is perhaps 
 too much to hope, that the geometrical arrangement of 
 primary particles will ever be perfectly known ; since even 
 admitting that a very small number of these atoms com- 
 bining together would have a tendency to arrange them- 
 selves in the manner I have imagined; yet, until it is 
 ascertained how small a proportion the primary particles 
 themselves bear to the interval between them, it may be 
 supposed that surrounding combinations, although them- 
 selves analogous, might disturb that arrangement, and in 
 that case, the effect of such interference must also be 
 taken into the account, before any theory of chemical 
 combination can be rendered complete. 
 
Thomson on Oxalic Acid. 41 
 
 EXTRACTS FROM A PAPER ON OXALIC 
 ACID. BY THOMAS THOMSON, M.D., 
 F.R.S.Ed* 
 
 Read Jan. 14, 1808. 
 
 Pp. 69-70. Oxalate of potash readily crystallizes in flat 
 rhomboids, commonly terminated by dihedral summits. 
 The lateral edges of the prism are usually bevelled. The 
 taste of this salt is cooling and bitter. At the temperature 
 of 60 it dissolves in thrice its weight of water. When dried 
 on the sand bath, and afterwards exposed in a damp 
 place, it absorbs a little moisture from the atmosphere. 
 
 This salt combines with an excess of acid, and forms 
 a superoxalate, long known by the name of salt of sorrel. 
 It is very sparingly soluble in water, though more so than 
 tartar. It occurs in commerce in beautiful 4-sided 
 prisms attached to each other. The acid contained in 
 this salt is very nearly double of what is contained in 
 oxalate of potash. Suppose 100 parts of potash; if the 
 weight of acid necessary to convert this quantity into 
 oxalate be x, then 2x will convert it into superoxalate. 
 
 P. 74, ... It appears that there are two oxalates 
 of strontian, the first obtained by saturating oxalic acid 
 with strontian water, the second by mixing together 
 oxalate of ammonia and muriate of strontian. It is 
 remarkable that the first contains just double the propor- 
 tion of base contained in the second. 
 
 * Philosophical Transactions, vol. 98 (for 1808), p. 63. 
 
42 Thomson. 
 
 EXTRACTS FROM THOMSON'S SYSTEM OF 
 CHEMISTRY.* 
 
 This difference between the density of the gases, 
 while their elasticity is the same, must be owing to one 
 of two causes : Either the repulsive fora \ or the density 
 of the atoms, differs in different gases. The first suppo- 
 sition is by no means probable, supposing the size and 
 density of the particles of different gases the same, and 
 indeed would but ill agree with the analogy of nature ; 
 but the second is very likely to be the true cause. And 
 if we suppose the size and density of the atoms of dif- 
 ferent gases to differ, this in reality includes the first 
 cause likewise ; for every variation in size and density 
 must necessarily occasion a corresponding variation in 
 the repulsive force, even supposing that force abstractedly 
 considered to be the same in all. 
 
 We have no direct means of ascertaining the density 
 of the atoms of bodies ; but Mr Dalton, to whose un- 
 common ingenuity and sagacity the philosophic world 
 is no stranger, has lately contrived an hypothesis which, 
 if it prove correct, will furnish us with a very simple 
 method of ascertaining that density with great precision. 
 Though the author has not yet thought fit to publish his 
 hypothesis, yet as the notions of which it consists are 
 original and extremely interesting, and as they are inti- 
 mately connected with some of the most intricate parts 
 of the doctrine of affinity, I have ventured, with Mr 
 
 * A System of Chemistry. By Thomas Thomson, M.D., 
 F.R.S.E., 3d edition, vol. iii., Edinburgh 1807, pp. 424-429 and 
 451-452. These extracts form a part of the first public exposition 
 of Dalton's views. 
 
Dalton's Hypothesis. 43 
 
 Dalton's permission, to enrich this work with a short 
 sketch of it.* 
 
 The hypothesis upon which the whole of Mr Dalton's 
 notions respecting chemical elements is founded, is this : 
 When two elements unite to form a third substance, it is 
 to be presumed that one atom of one joins to one atom 
 of the other, unless when some reason can be assigned 
 for supposing the contrary. Thus oxygen and hydrogen 
 unite together and form water. We are to presume that 
 an atom of water is formed by the combination of one 
 atom of oxygen with one atom of hydrogen. In like 
 manner one atom of ammonia is formed by the combina- 
 tion of one atom of azote with one atom of hydrogen. If 
 we represent an atom of oxygen, hydrogen, aud azote, by 
 the following symbols, 
 
 Oxygen - - Q 
 
 Hydrogen - Q 
 
 Azote -Wfcri***- - Q) 
 
 Then an atom of water and of ammonia will be repre- 
 sented respectively by the following symbols : 
 
 Water QQ 
 
 Ammonia - - Q(J) 
 
 But if this hypothesis be allowed, it furnishes us with a 
 ready method of ascertaining the relative density of 
 those atoms that enter into such combinations; for it 
 has been proved by analysis, that water is composed of 
 
 * In justice to Mr Dalton, I must warn the reader not to decide 
 upon the notions of that philosopher from the sketch which I have 
 given, derived from a few minutes' conversation, and from a short 
 written memorandum. The mistakes, if any occur, are to be laid 
 to my account, and not to his ; as it is extremely probable that I 
 may have misconceived his meaning in some points. 
 
44 Thomson. 
 
 85! of oxygen and 14^ of hydrogen. An atom of 
 water of course is composed of 85^ parts by weight of 
 oxygen and 14^ parts of hydrogen. Now, if it consist 
 of one atom of oxygen united to one atom of hydrogen, 
 it follows, that the weight of one atom of hydrogen is 
 to that of one atom of oxygen as 14^ to 85^, or as i to 
 6 very nearly. In like manner an atom of ammonia 
 has been shown to consist of 80 parts of azote and 20 
 of hydrogen. Hence an atom of hydrogen is to an 
 atom of azote as 20 to 80, or as i to 4. Thus we have 
 obtained the following relative densities of these three 
 elementary bodies. 
 
 Hydrogen - - i 
 
 Azote 4 
 
 Oxygen - - 6 
 
 We have it in our power to try how far this hypothesis 
 is consonant to experiment, by examining the combina- 
 tion of azote and oxygen, on the supposition that these 
 bodies unite, atom to atom, and that the respective den- 
 sities of the atoms are as in the preceding table. But 
 azote and oxygen unite in various proportions, forming 
 nitrous oxide, nitrous gas, and nitric acid, besides some 
 other compounds which need not be enumerated. The 
 preceding hypothesis will not apply to all these com- 
 pounds ; Mr Dalton, therefore, extends it farther. 
 Whenever more than one compound is formed by the 
 combination of two elements, then the next simple com- 
 bination must, he supposes, arise from the union of one 
 atom of the one with two atoms of the other. If we 
 suppose nitrous gas, for example, to be composed of one 
 atom of azote, and one of oxygen, we shall have two new 
 compounds, by uniting an atom of nitrous gas to an 
 atom of azote, and to an atom of oxygen, respectively. 
 If we suppose farther, that nitrous oxide is composed of 
 an atom of nitrous gas and an atom of azote, while 
 
Dalton's Hypothesis. 45 
 
 nitric acid consists of nitrous gas and oxygen, united 
 atom to atom ; then the following will be the symbols 
 and constituents of these three bodies : 
 
 Nitrous gas - QD 
 
 Nitrous oxide - - 
 
 Nitric acid 
 
 The first gas consists only of two atoms, or is a binary 
 compound, but the two others consist of three atoms, 
 or are ternary compounds ; nitrous oxide contains two 
 atoms of azote united to one of oxygen, while nitric 
 acid consists of two atoms of oxygen united to one of 
 azote. 
 
 When the atoms of two elastic fluids join together to 
 form one atom of a new elastic fluid, the density of this 
 new compound is always greater than the mean. Thus 
 the density of nitrous gas, by calculation, ought only to 
 be 1.045; but its real density is 1.094. Now as both 
 nitrous oxide and nitric acid are specifically heavier than 
 nitrous gas, though the one contains more of the lighter 
 ingredient, and the other more of the heavier ingredient 
 than that compound does, it is reasonable to conclude, 
 that they are combinations of nitrous gas with azote and 
 oxygen respectively, and that this is the reason of the 
 increased specific gravity of each ; whereas were not this 
 the case, nitrous oxide ought to be specifically lighter than 
 nitrous gas. Supposing, then, the constituents of these 
 gases to be as represented in the preceding table, let us 
 see how far this analysis will correspond with the densi- 
 ties of their elements, as above deduced from the compo- 
 sitions of water and ammonia. 
 
 Nitrous gas is composed of i.oo azote and 1.36 
 oxygen, or of 4 azote and 5.4 oxygen. 
 
 Nitrous oxide, of 2 azote and 1.174 oxygen, or of 
 4 + 4 azote and 4.7 oxygen. 
 
46 Thomson. 
 
 Nitric acid, of i azote and 2.36 oxygen, or of 4 azote 
 and 4.7+4.7 oxygen. 
 
 These three give us the following as the relative den- 
 sities of azote and oxygen : 
 
 Azote. Oxygen. 
 
 4 : 5-4 
 : 4.7 
 : 4.7 
 
 The mean of the whole is nearly 4:5; but from pre- 
 ceding analyses of water and ammonia, we obtained their 
 densities 4 : 6. Though these results do not correspond 
 exactly, yet the difference is certainly not very great, and 
 indeed as little as can reasonably be expected, even sup- 
 posing the hypothesis is well founded, if we consider the 
 extreme difficulty of attaining accuracy in the analysis of 
 gaseous compounds. If ammonia were supposed a 
 compound of 83 azote and 17 hydrogen, instead of 80 
 azote and 20 hydrogen, in that case the density of azote 
 would be five instead of four, and the different sets of 
 experiments would coincide very nearly. Now it is 
 needless to observe how easy it is, in analysing gaseous 
 compounds, to commit an error of 3 per cent, which is 
 all that would be necessary to make the different num- 
 bers tally. 
 
 On the supposition that the hypothesis of Mr Dalton 
 is well founded, the following table exhibits the density 
 of the atoms of the simple gases, and of those which 
 are composed of elastic fluids, together with the symbols 
 of the composition of these compound atoms : 
 
 Hydrogen - i 
 
 (T) Azote - 5 
 
 O Oxygen - - 6 
 
 Q Muriatic acid - - 9 
 
 v .-aU/vt-AX^i f 
 
Dalian's Hypothesis. 47 
 
 ---- 7 
 
 Ammonia - 6 
 
 0Q) Nitrous gas - 1 1 
 
 (DOCD Citrous oxide - - 16 
 
 O(DO Nitric acid - 17 
 
 QQQ Oxymuriatic acid - .24 
 
 UwvJ Hyperoxymuriatic acid - 27 
 
 * * * 
 
 Oxygen and nitrous gas, when brought into contact, 
 immediately unite and form a yellow-coloured vapour. 
 From the experiments of Dalton, it appears that these 
 gases are capable of uniting in two different proportions. 
 One hundred measures of common air, when added to 
 36 measures of nitrous gas in a narrow tube over water, 
 leave a residue of 79 inches ; and one hundred measures 
 of common air, admitted to 72 measures of nitrous gas 
 in a wide glass vessel over water, leave likewise a residue 
 of 79 measures.* According to these experiments, 21 
 cubic inches of oxygen gas is capable of uniting with 36 
 and with 72 cubic inches of nitrous gas; or 100 inches 
 of oxygen unite with 171.4 and with 342.8 inches of 
 nitrous gas. If we apply Mr Dalton's hypothesis, stated 
 in a former Section, to these combinations, we shall have 
 the first composed of one atom of oxygen united to one 
 atom of nitrous gas ; the second, of one atom of oxygen 
 united to two atoms of nitrous gas. The first appears to 
 be the substance usually distinguished by the name of 
 nitric acid ; .the second is nitrous vapour, or nitric acid 
 saturated with nitrous gas. The following will be the 
 
 * Phil. Mag. xxiii. 351. 
 
48 Thomson. 
 
 symbols denoting the composition of an atom of each, 
 and the density of that atom, obtained by adding 
 together the numbers denoting the density of each of the 
 constituent atoms. 
 
 Density. 
 
 O(DO Nitric acid - - 17 
 
 Nitrous va P ur 28 
 
 The first is a triple compound, and can only be resolved 
 into nitrous gas and oxygen, or into azote and oxygen ; 
 but the second is a quintuple compound, and may be 
 resolved into nitrous oxide and oxygen, nitrous gas and 
 oxygen, nitric acid and nitrous gas, oxygen and azote. 
 
 THE DARIEN PRESS, BRISTO PLACE, EDINBURGH.