176 



PROPORTIONS DETERMINATE. 



Lavoisier. 



Berthollet. 



chemical speculations; no one listened to him. .By 

 degrees, however, the system of Lavoisier was conso- 

 lidated: finally adopted by its most stubborn oppo- 

 nents, it became generally known ; and the greater 

 part of our present chemists have studied the science 

 under no other form but that which Lavoisier's hypo- 

 thesis presents. The attention which, during five and 

 twenty years, had been directed to this single point, 

 was at length divided ; and the luminous rays dis- 

 seminated in the works of hostile or prior writers 

 beamed forth anew. It may thus be affirmed, that 

 the birth and consolidation of the antiphlogistic sys- 

 tem put a stop, for a time, to the investigation of 

 chemical proportions, which originated at the same 

 period. 



Lavoisier himself advanced nothing very decided 

 upon this point. He observed that there is one spe- 

 cies of combination always limited to fixed propor- 

 tions, and another which may take place in variable 

 proportions ; and he thought that being of a different 

 nature, they ought to be carefully distinguished. He 

 proposed to give them different names ; he called the 

 first dissolution, the second solution. A combination of 

 the oxide of iron, with sulphuric acid, is an example 

 of dissolution ; but when the sulphate of iron is meit- 

 ed by water it forms a solution. 



Some time after the death of Lavoisier, M. Berthol- 

 let, the most distinguished of his fellow-labourers, pub- 

 lished a work under the title of Essai de Statique Chi- 

 mique, in which he considered affinities, and the pheno- 

 mena that depend on them, with a truly philosophic 

 eye, and to the admiration of all chemists. He en- 

 deavoured to prove that the active forces are not so 

 multifarious as the diversity of the phenomena might 

 lead us to suppose; and he made it probable that che- 

 mical affinities depend entirely upon a single force ; 

 just as the force which causes a body to fall towards 

 the earth is the same as that which retains the planets 

 in their orbits. In a word, he conjectured that one 

 day we should be enabled to calculate the former as 

 accurately as, from a distant period, we have calculated 

 the phenomena dependent on the other. 



Berthollet, proceeding farther, attempts to prove that 

 solutions depend on exactly the same affinity as disso- 

 lutions ; the difference consisting merely in the degree 

 of energy possessed by this affinity, which is smaller 

 in the former case than in the latter. Elements, he 

 maintained, have a minimum and a maximum, beyond 

 which they cannot enter into combination ; but be- 

 tween these two points they unite in every proportion, 

 no other limit to their union being fixed. Whenever 

 they happen to combine in fixed proportions between 

 those two points, their union is due to other circum- 

 stances ; for most part to cohesion, which renders the 

 combination insoluble ; or to expansion, which renders 

 it gasiform. If in combining they undergo a high de- 

 gree of condensation, the proportions in which they 

 unite are always invariable ; and for this reason gase- 

 ous substances never combine except in fixed propor- 

 tions : hydrogen with oxygen, for example ; azote 

 with oxygen, and so on. But when, after combination, 

 the elements continue in the same degree of density 

 as before it, they may unite in all proportions between 

 the maximum and the minimum. The regularity of 

 proportion subsisting among the elements of acids, 

 salts, &c. depends, according to this theory, on nothing 

 but the condensation of the gaseous form, or on crys- 

 tallization. Berthollet made a multitude of expe- 

 riments to prove the truth of these ideas ; and though 



5 



it is now believed that his opinions are not well found- 

 ed, he must be allowed to have expressed them, ag 

 well as their- proofs, with a sagacity and philosophic 

 distinctness at once convincing and uncommon. He 

 examined the experiments of Richter, and found num- 

 bers different from his. He first disputed, but after- 

 wards admitted, the mutual relation among bases ob- 

 served already by Wenzel, though he attributed it to 

 cohesive force, in other words, to crystallization. 



A philosophical chemist requires to be seconded by 

 the talent of wisely choosing his experiments, and of 

 executing them with address ; otherwise, perpetually 

 deceived by them, he will build upon false foundations. 

 So it has happened to this illustrious chemist. His ex* 

 periments, viewed as exact analyses, have always given 

 results extremely inaccurate, so that scarcely one of 

 them is just; and in this point of view Bertholle% has 

 been still less fortunate than Richter. Berthollet ob- 

 served, and proved indisputably, that elementary par- 

 ticles act not only according to the degree of their af- 

 finity, but also according to their mass. This pheno- 

 menon, however, does not happen except when the 

 bodies that act, as well as the products of their mutual 

 action, all continue mixed in solution, or under a liquid 

 form. As Berthollet admits no other difference be- 

 tween solution and chemical combination but the de- 

 gree of affinity, it seems probable that his mistake with 

 regard to this point has occasioned all the rest. 



It has lately been shown, by detailed and exact ex- 

 periments, that Lavoisier was not wrong in considering 

 these phenomena as different. It is known, for exam- 

 ple, that pure lime and magnesia combine with water, 

 for which they have a great affinity ; but the one is 

 very sparingly soluble in water, whilst the other is not 

 soluble at all. Several bodies which contain great 

 quantities of water in chemical combination, the me- 

 tallic hydrates for example, the carbonates of various 

 earths, &c. are not at all soluble in water ; whilst other 

 bodies which do not combine chemically with water 

 are abundantly soluble in it; such as saltpetre, and 

 culinary salt. When a substance combines chemically 

 with water, it disengages caloric ; when merely dis- 

 solved in water, its caloric is absorbed, and the tem- 

 perature falls. A body possessing the property of 

 combining with water, and at the same time soluble 

 in it, first evolves heat, and afterwards cold. These 

 entirely opposite phenomena must arise from a differ- 

 ent cause ; and consequently there must be some cir- 

 cumstance in solution which does not find place in che- 

 mical combination, or inversely. 



M. Berthollet's opinions were first examined by M. Proust. 

 Proust. He proved, from a series of ingenious experi- 

 ments, that the new theory, when applied to any thing 

 but solutions, and mixtures in a liquid state, led to 

 considerable errors. It admitted, for example, that 

 metals, in combining with oxygen, exhibit an infinite 

 number of degrees of oxidation, between their minimum 

 and maximum. Proust chose antimony and iron to 

 show that this is not the case ; and that, on the con 

 trary, those metals do not combine with oxygen in 

 more than two proportions ; but that, if their minimum 

 oxide is exposed to the action of oxygen, a portion be 

 ing converted into the maximum oxide, remains me- 

 chanically mixed with the former. From which it ap- 

 pears, said Proust, that Berthollet has deceived him- 

 self by considering mechanical mixtures of the two 

 oxides as particular degrees of oxidation. Proust ex- 

 tended his experiments to the metallic sulphurets, and 

 found that a similar principle may be applied to them 



