42 Dr. Sertumer on the Combination of Acids (July, 



strongest bases are not capable of disengaging it. I name these 

 compounds theimates and subthermates (from the analogy of 

 hydrates and sul/ln/drakes), because in them the heat is as notable 

 an ingredient as water is in the hydrates. 



Many compounds to which the name of hydrate is given do not 

 conespond with these characters ; for a true hydrate is a com- 

 pound of a substance with thennate of ice (water). The heat in 

 these compounds is a more important and more active ingredient 

 than the ice. Such are the true hydrates. From them we must 

 distinguish the compounds which do not contain heat as a con- 

 stituent, but simply ice ; as, for example, the, crystals of salts. 

 This circumstance explains clearly and fully why different bodies 

 when they unite with water evolve a high degree of cold or of 

 heat. Suppose a substance which has a strong attraction for 

 water, hydrate of ice (as crystallized muriate of lime), to be 

 placed in contact with ice, the salt, in consequence of its attrac- 

 tion for water, obliges the heat (to speak, figuratively), which is in 

 the neighbourhood, to enter into combination -with the ice, and 

 form a hydrate of ice, in order to satisfy this attraction. The 

 salt thus saturated with thennate of ice constitutes a true hydrate. 

 Consequently the cold produced must be the more violent the 

 greater the attraction of the salt for the thennate and the less 

 heat there is in the neighbourhood ; that is to say, the colder 

 the mixture was. If, on the other hand, a substance, as lime, 

 which has a stronger attraction for ice, be placed in contact with 

 the thermate of ice, it separates the heat from the thermate, and 

 unites itself with the ice in its place. Hence the solid hydrate 

 of lime is not a true hydrate, but a compound of lime and ice. 

 This is the reason why heat is evolved when such a compound 

 is formed. The compounds which the oxide of hydrogen forms 

 in the state of ice must be carefully distinguished from, the 

 hydrates or the compounds into which water enters in the state 

 of water. We shall see hereafter that there are other subdivi- 

 sions of these last. 



I come now again to the ther mates. They may be very well 

 compared with the salts. Thus in neutral compounds of heat 

 with free anhydrous acids, as thermate of carbonic acid, of sul- 

 phurous acid, &c. the heat is the only basis. There exist also 

 compounds of heat and hydrous acids, which may be more or 

 less saturated with water; and in them the water commonly 

 performs the part of the principal bases. The vapour of the 

 sulphuric acid, which does not smoke, and which of course is 

 fully saturated with water, is the thermate of hydrous sulphuric 

 acid. On the other hand, the gas or vapour of the dry sulphuric 

 acid is a compound of heat with sulphuric acid not fully satu- 

 rated with water. In this dry, volatile, sulphuric acid, crystal- 

 lized like amianthus, the heat and the water appear to constitute 

 equally the basis. Hence it may be considered as a subhydro- 

 therma re of sulphuric acid, or as sulphuric acid united at once 



