CHEMISTRY. 570 CHEMISTRY. tjiplied to water and the oxides of llie metals. True enough, in his list of elements (1787) Lavoisier included also light and heat and the compounds potash, soda, and lime; on the other hand, he considered the element chlorine as a compound containing oxygen. But this did not interfere with further progress. Tlie first bridge of clicmistry was firmly established, and the lingering errors were rectified (mainly by Sir Humphry Davy) early in the Nineteenth Centuri)'. The development of another corre- spondence — viz. that between the hypothesis of the atomic constitution of matter and the quan- titative composition of substances — was already noted in a jireoeding section of this article. Here it may be observed that the law of multiiile pro- portions was first discovered bv Kichter ( 17ti2- 1807). and that Proust ( 1754"-1826) continued Richter's researches and clearly demonstrated the law in course of a controversy with Herthol- let. Daltoii (1804) re-discovered the law de- ductively and then proved it experimentally; he was thus the first to establish a rational coniiec- tibn between the old atomic hypothesis and the facts of chemical composition. After the relation between the knovra metals and their oxides was established, Lavoisier him- self, and others, began to suspect the true na- ture even of oxides whose metals were not yet known in the free state, and attempts began to be made to decompose these oxides so as to iso- late their metallic elements. About the begin- ning of the Nineteenth Century. Sir llumj/hry Davy (1778-182!)) undertook to investigate the efl'ect of the galv.anio current on chemical com- jiounds. In 1807-08 he succeeded in decompos- ing caustic potash and caustic soda, obtaining from them the metals potassium and so<lium. About the same time Seebeek similarly decom- posed the oxides of calcium, barium, strontixim, and magnesium, obtaining these metals in the form of their amalgams — i.e. combinations with mercury. From these amalgams Davy isolated the metals themselves and gave them their pres- ent names. From the metals Dav7' turned his genius to the non-mctallio eleiiieuts. Chlorine, known since 1774, remained unrecognized as an clement, and was generally considered as the oxide of hydrochloric acid. In 1811 Davy clear- ly demonstrated its elementary nature: and when, soon aftervvards, Courtois discovered io- dine. Davy showed that this substance, too, so similar to chlorine, must be considered as an clement. Davy also was the first to demonstrate clearly the elementary nature of nitrogen, and even of fluorine (from the similarity of hydro- fluoric to hydrochloric acid, and of the fluorides to the chlorides), although the latt<>r element vas not yet knowTi in the free state, and re- mained imknown until 1887. The value of Davy's contributions can be readily appreciated if we remember that the substances he was deal- ing with are among the commonest in the entire range of chemistry, and if we imagine how much confusion would suddenly ensue in all depart- ments of the science if we were to forget their existence or their true nature. Du.i.issr. On the basis of his electrolytic in- vestigations. Davy also constructed an electro- chemical theory which was subsequently modi- fied and extended by Berzelius. According to Davy (1807). when the atoms of different ele- ments come into contact, they become charged with the opposite forms of electricity, by whose attractive force they are held together, constitut- ing chemical compounds. Berzelius's theory was as follows : The atom of each element does not become charged with electricity on coming in contact with other atoms, but is charged, wheth- er combined with other atoms or not. With re- spect to the electrical charges of their atoms, the elements form an 'electro-chemical order.' oxygen being the most electro-negative, potas- sium the most electropositive, and hydrogen di- viding the electro-negative from the electro-posi- tive elements. All bases are produced by the combination of oxygen with electro-positive, all acids by the combination of oxygen with electro- negative elements. Yet ba.ses and acids are not altogether neutral : in the former positive elec- tricity, in the latter negative electricity, pre- dominates. This is wliy bases and acids sliow no mutual chemical indill'crence, but combine to form salts. When the terminals of a sufliciently powerful galvanic battery are immersed in the solution of a salt, the base of the latter is at- tracted more strongly by the negative terminal than by the acid, and the acid is attracted more strongly by the positive tenninal than by the liase: hence electrolysis ensues, the base being deposited on the negative, the acid on the positive, tenninal. In hrief, Berzelius main- tained ( 1 ) that oxygen is an indispensable con- stituent of b.ases, acids, and s.alts; (2) that bases, acids, and salts have a dual constitution, each being made up of an electro-positive and an electro-negative part : (8) that chemical allinity is nothing but the mutual attraction of opposite forms of electricity. In the first of these prin- ciples Berzelius followed Lavoisier, for years re- fusing to acccjit Davy's view that chlorine and nitrogen were elements, and that tlieir com- pounds with hydrogen — namely, hydrochloric acid and .ammonia — although respectively an acid and a base, contained no o.xygen. The stru(!ture of the entire theory became somewhat shaky when the correctness of Davy's views was finally recogiiizcd by all. including IJerzelius him- self (1820). Nevertheless, Berzelius. ami with him the entire chemical world, continued to ad- here to the electro-chemical theory, and thus a strictly dualistic conception of compounds con- tinued to reign in the science. The thirties, how- ever, brought much new evidence against Ber- zelius's principles. First of all it was recog- nized that electrolysis breaks up a salt, primarily not into two oxides, but into a free metal and an acid radicle. For example, potassium sul- phate is broken up. primarily not into K.O and SO;;, but into K; and the radicle SO,. This made it evident that sulphuric acid was not SO,, but H.SO, (i.e. SO, chemically combined with H.O), because the SO, radicle was seen to be the true acidic component of potassium sulphate. Two important conclusions thus thrust themselves upon chemists: (I) .-
acid is not a binary
compound of oxygen with an electro-negative element, but a combination of hydrogen with an electro-negative radicle: (2) a salt is not a com- pound of two oxides (e.g. K.O.SO;), but a com- bination of a metallic element with the electro- negative radicle (e.g. SO,) of an acid. Tlie first of these conclusions, together with Davy's discovery that hydrochloric acid contained hy- drogen but no oxygen, indicated that not oxy- gen, but hydrogen, is an indispensable com-
