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CHEMISTRY 365 incalculable. Since the latter has become a matter of popular education, the methods of teaching it have been made subjects of special study and have been vastly improved. The immense influence which chemistry now every- where exerts upon arts and manufactures, and which is one of the characteristics, not only of the science itself, but of the civilization of the 19th century, may be traced directly back to the labors of Berthollet, Guyton, and their associates. In connection with these, Fourcroy deserves mention. He devised the plan of the system of instruction introduced into France by Napoleon, and did good service as a lecturer and writer. Attention having been specially directed to quantitative analysis by Lavoisier and Bergman, many chemists now occupied themselves with it. Of these, Klap- rbth (1743-1817) in Germany, Vauquelin (1763 -1829) in France, and Proust (died 1826) in Spam, exerted the most influence. Klaproth was the first German chemist who admitted the correctness of Lavoisier's views. He did much to diffuse them among his countrymen, in spite of the national feeling brought to bear against the " French system." But his chief merit is as an analyst. He first introduced the custom of publishing the results of quantitative analyses, as found directly by experiment. Any loss or excess had previously been dis- tributed among the several ingredients, and such corrected values alone published, leaving no clue from which other chemists might judge of the accuracy of the statement. This led to numerous errors, many false notions of the composition of bodies having long been held on the authority of a single analyst. The utility of Klaproth'a system of publishing details has been most clearly proved by the fact that many of his own analyses have coincided with cor- rections which it has since been found neces- sary to apply to the inferences he had himself drawn from them. Klaproth devised the more common methods of decomposing insoluble minerals, which are still used. He pointed out the influence which the gradual destruc- tion of the utensils in which analyses are made exerts upon the results obtained, and called attention to the necessity of applying a correc- tion on account of it. Many of the methods now used for separating bodies from each other have come down from him. He discovered the oxides of uranium, zirconium, cerium, and tita- nium, and made many other important obser- vations. Vauquelin performed a great amount of analytical labor, especially in regard to min- erals. With Klaproth he had widely extended the field of analysis. But although they were agreed that most bodies have a constant or near- ly constant composition, they were silent when Berthollet advanced an opinion that the reverse is often the case. Berthollet admitted but few compounds of constant composition in one pro- portion. In most bodies he thought the con- stituents capable of uniting in any proportion between two limits. Thus, iron could unite with oxygen in any proportion between prot- oxide and peroxide. This view did much mis- chief. Every false analysis supported itself, while it seemingly supported the theory, upon it, by admitting that the combining proportions of the ingredients were variable. Proust de- servedly won great reputation by proving that these supposed intermediate compounds do not exist in so many varying proportions. He de- monstrated that when two substances unite in several proportions, the compounds formed are but few and are separated from each other by in- tervals, never gradually shading into each other. He explained correctly the composition of red lead, of magnetic oxide of iron, &c. He pointed out the errors committed by previous investiga- tors of the subject, and the necessity of not con- founding chemical compounds with mechanical mixtures. His views were soon received as correct by chemists, in spite of the opposition of Berthollet. He also carefully studied several metals and hydrates of metallic oxides, distin- guished grape from cane sugar, &c. Proust and his predecessors, in determining the composition of bodies, sought only to ascertain how much of each ingredient was contained in a constant weight, usually 100 parts of the compound, thus referring the weight of the ingredient to that of the compound. The science had thus been greatly advanced, but still more important discoveries were made when chemists began to consider the relations which the weights of the several ingredients of a body bear to each other, and to investigate how much of one substance is required to replace another in a compound. The idea of chemical equivalents thus arose, and it was soon recognized that chemical combina- tions take place not only in constant but also in simple relations of weight. Wenzel in 1777, and Eichter in 1792, in Germany, were the first who endeavored to call attention to this sub- ject. The former explained the fact that when two neutral salts mutually decompose each oth- er, the resulting mixture is still neutral, by ad- mitting that a quantity of either base sufficient to neutralize one acid could also neutralize the other acid. He moreover showed that the rel- ative weight of two bases which neutralize the same quantity of acid remains constant, no mat- ter what acid may be used. Arguing from "Wenzel's law, Richter showed that, in accord- ance with it, the composition of all the neutral salts of one acid and of any one salt of any other acid having been ascertained by analysis, the composition of any other salt of this acid could be calculated. He also showed that numbers could be affixed to the acids and bases which would express the relation of weight in which they combine with each other to form neutral salts, and even constructed such tables of equiv- alents. The views of both these chemists were neglected until the publication of the atomic theory of Dalton (1766-1844) recalled the atten- tion of chemists to them; when they exerted no inconsiderable influence in establishing Dalton's doctrine. This last was much more extended