SOS 



CHEMISTRY. 



CHEMISTRY. 



806 



air, now called oxygen gas. This important accession to chemical 

 science was made on the 1st of August, 1774. He procured it by 

 strongly heating red oxide of mercury, formed by the action of heat 

 and air upon the metal, and collecting the gas which was evolved from 

 it. The consequences of this discovery would require a volume for 

 description ; it has served as the basis for all that is known respecting 

 the nature of the atmosphere, water, acids, and alkalies; and the 

 nature of combustion has been greatly illustrated by it. 



Sulphurous acid, fluosilicic acid, hydrochloric acid, and ammonia 

 were first made known in the gaseous state by Dr. Priestley ; he dis- 

 covered nitrous oxide gas, and first obtained carbonic oxide gas, the 

 nature of which however he mistook. He did not discover hydrogen 

 gas, but his experiments upon it are interesting ; he pointed out the 

 existence of carburetted hydrogen gas, though he did not make many 

 experiments upon it. 



The action of electricity on various compound gases was examined 

 by him, and he showed that an acid is formed when sparks are passed 

 through a confined portion of atmospheric air : this fact served as the 

 basis of Cavendish's discovery of the composition of nitric acid. In the 

 same way, the increase of bulk which he found to take place by the 

 action of the same agent on ammoniacal gas led Berthollet to determine 

 the nature of it. His experiments on the amelioration of atmospheric 

 air by the process of vegetation are highly curious, and have been 

 repeated and confirmed by subsequent investigations. His work 

 entitled ' Experiments and Observations on different kinds of Air ' con- 

 tains a vast number of experiments, from which various inferences 

 might be drawn, which he seems, in his rapid career of discovery, him- 

 self to have overlooked : such are those just mentioned ; and the 

 composition of atmospheric air and water might be added to the list. 



His additions to the means previously known for experimenting on 

 gaseous bodies have afforded the greatest facilities to those who have 

 followed him : such are the invention of the pneumatic trough, and 

 the substitution of mercury for water in the case of those gases which 

 are soluble iu the latter fluid. To conclude with the observations of 

 Sir H. Davy : " Chemistry owes to him some of her most important 

 instruments of research, and many of her most useful combinations ; 

 and no single person ever discovered so many new and curious 

 substances." 



The works of Torbern Bergman (born in 1735, died in 1784) have 

 been collected and translated into English. The first paper which he 

 published was in 1774, ' On the Aerial Acid,' now called carbonic acid 

 gas. If the contents of this paper be compared with the previous one 

 of Cavendish on the same subject, it will be seen that the latter had 

 anticipated Bergman on many of the more important facts. No notice, 

 however, is taken of Cavendish's experiments in it. He afterwards 

 published papers on the ' Analyses of Mineral Waters,' and though the 

 methods which he adopted are by no means accurate, they were pre- 

 ferable to any which had been previously used. 1 



He published a paper on oxalic acid, of which however the discovery 

 is said to be due to Scheele. It will be scarcely possible to enumerate 

 even the various papers of Bergman, and much less to give an analysis 

 of their contents. His ' Essay on Electric Attractions ' is however a 

 work of importance, and requires a more detailed notice. The inten- 

 tion of the author was to point out the nature of chemical affinity, 

 and to account for the anomalies which that complicated subject 

 appears to present. He adopts it as a principle that chemical combi- 

 nation is the result of an absolute force. Berthollet attempted to show 

 that this conclusion is erroneous, and though it must be admitted that 

 there are various circumstances which modify the action of this power, 

 we are not so nearly without a guide to just conclusions as the 

 experiments and opinions of Berthollet would lead us to admit. 



Bergman published tables in fifty-nine columns, in which he showed 

 the relative attraction of bodies, or what he terms elective affinity. As 

 the order of decomposition often varies, according as it is made in the 

 dry way or the moist, each of the fifty-nine columns was divided into 

 two ; the first exhibiting the order of decompositions in the moist, and 

 the second in the dry way. He also stated various cases of double 

 decomposition. These tables are constructed upon the now well-known 

 principle, that any substance, whether acid, alkali, or metallic oxide, 

 being placed at the head of a column, and others under it, such sub- 

 stance has the greatest affinity for that next to it, and for the rest, 

 according to the nearness of their place. 



It has been already observed, that Bergman's processes for analysing 

 mineral waters were more correct than any which had been previously 

 adopted, and although his experiments on the analysis of precious 

 tones are far removed from perfection, yet they possess the rudiments 

 of the methods which are now adopted. He first proposed the ana- 

 lysing of minerals by combining them with the fixed alkalies, by which 

 they were rendered partially soluble in water, and totally so either in 

 that fluid or iu an acid. 



Hu found fulminating gold to yield ammonia; and he explains the 

 detonation to arise from the sudden decomposition of that gaseous 

 body. 



The discoveries which next claim attention are those of Charles 

 William Scheele, who waa born at ytralsund in \l\'l, and died in 1780. 

 Like Priestley, Scheele began his experiments under very unfavour- 

 able circumstances with respect to apparatus and the means of 

 procuring it. 



Scheele, observing that air was requisite to combustion, subjected it 

 to analysis. He found that certain substances, especially what was 

 then termed liver of sulphur, and now sulphuret of potassium, when 

 exposed to a given bulk of air, diminished it to about four-fifths of the 

 original quantity ; he found also that the flame of burning sulphur and 

 of hydrogen gas produced the same effect. Without any acquaintance 

 with what Priestley had previously done, he obtained, by various pro- 

 cesses, oxygen gas, which he termed empyreal air ; and he showed that 

 this air was absorbed by liver of sulphur; and that upon adding 

 fresh empyreal air to that left unacted upon by it atmospheric air was 

 reproduced. 



His experiments on the nature of air were followed by some on heat 

 and light, and he gave the name of radiant heat to that portion of it 

 which emanates from hot bodies, and, as he found, in right lines. He 

 observed the blackening effect which is produced by the sun's rays on 

 chloride of silver, and that the violet rays produce this effect most 

 speedily. He made experiments on Homberg's pyrophorus, and 

 showed that ammonia alum is incapable of forming it. In his disser- 

 tation on manganese, he made the discovery of chlorine gaa, or, as he 

 called it, dephlogisticated marine acid. His essays on fluor spar con- 

 tained several valuable facts, but he committed the error of supposing 

 that the silica which he obtained in his operations, from the retort, 

 was formed by the combination of water and fluoric acid. He pointed 

 out the difference between plumbago and sulphuret of molybdenum ; 

 and he first described the molybdic and arsenious acids, and formed a 

 compound of the latter with oxide of copper, arsenite of copper, which 

 has since been extensively used as a pigment, under the name of 

 Scheele's or mineral green. He made experiments on milk, and sugar 

 of milk ; and the acid of the sugar of milk, now called lactic acid, was 

 noticed by him. He gave a method of obtaining citric, tartaric, gallic, 

 and some other vegetable acids ; and published essays on tungsten, 

 ether, calomel, benzoic acid, and urinary calculi, all of which contain 

 valuable information. 



He particularly examined the colouring matter of Prussian blue, 

 which was nearly his last contribution to chemical science. The sub- 

 ject waa one of great difficulty, considering that it involves the agency 

 of nitrogen, which had not long been discovered. He treats the subject, 

 however, with his usual sagacity ; and having obtained what is now 

 called prussic or hydrocyanic acid, he stated several of its properties. 

 Besides the discoveries which have been enumerated, it is to Scheele 

 that we are indebted for the first knowledge of baryta and of the 

 character of manganese. 



Antoine Laurent Lavoisier was born in Paris in 1743, and died a 

 victim to the revolution in 1794. Although the original discoveries of 

 Lavoisier have less merit than those of Priestley and Scheele, yet his 

 contributions to the science are numerous and important, especially as 

 to what regards its theory. His * Elemens de Chiruie ' were published 

 in 1789. In this work he considers heat as a subtile fluid or a material 

 substance, which he calls caloric. He argues that the different forms 

 of matter depend in general upon the quantity of caloric which they 

 contain. His analysis of atmospheric air, though conducted perhaps 

 on more philosophical principles, does not offer so great precision of 

 results as those deducible from the very simple experiment of Priestley ; 

 but it must be admitted that they had the merit of settling the question 

 as to the nature of the atmosphere. 



Van Helmont, and after him Macquer, had employed the term gas to 

 denote all elastic fluids which differ from atmospheric air. This word 

 Lavoisier also adopted ; and as he found that the portion of the atmos- 

 phere which supported animal life also entered into the composition of 

 acids, he called it oxygen gas; the other constituent of the air ho 

 called, from its fatal effects upon animal life, azotic gas, now called 

 nitrogen, a name derived from its producing nitric acid. 



Lavoisier and his coadjutors effected various improvements in 

 chemical nomenclature, most of which remain in use at present. The 

 nature of the diamond had excited the attention of the Florentine 

 Academy as early as 1090 ; the subject was resumed by Lavoisier, who 

 proved, that when air was excluded it underwent no change ; on the 

 other hand, he showed, that by burning it in oxygen gas carbonic acid 

 was formed, and hence he argued, what has since been more strictly 

 demonstrated, that the diamond, in its chemical nature, is similar to 

 common charcoal. 



In adverting to the solution of metals in acids, he notices the 

 necessity of their oxidisement previously to it; and hence he argues 

 the probability that the alkaline earths are metallic oxides, the oxygen 

 serving as a bond of union between them and the acids : this sagacious 

 remark was verified by the discoveries of Davy. In his additional 

 observations on the combinations of oxygen, he mentions the condi- 

 tions necessary for its union with different bodies ; the compounds 

 arising from the union of various combustible bodies are also treated 

 of, and those of the acids and some other compound substances. Sir 

 H. Davy remarks, that " Lavoisier must be regarded as one of the most 

 sagacious of the chemical philosophers of the last century; indeed, 

 except Cavendish, there is no other inquirer who can be compared to 

 him for precision of logic, extent of view, and sagacity of induction. 

 His discoveries were few, but he reasoued with extraordinary correct- 

 ness upon the labours of others. He introduced weight and measure, 

 and strict accuracy of manipulation into all chemical processes. His 

 mind was unbiassed by prejudices ; his combinations were of the most 



