1813.] Definite Proportions in Chemical Combinations. 171 



Number of Weight of an 



atoms. integrant particle. 



159. Hydrateofperoxidel { f + j w 18 . 969 x 



or tin J 



160. Hydrate of duetO ln + 2w Tm y 



oxide or nickel ) 



161. Hydrate of deut-j le + J w 1Q ^ 5Q , 



oxide or cobalt J 



162. Hydrate of protO lm+lw 9 . 262 a 



oxide or manganese . . J 



163. Hydrate of oxide of \ j Q , j w 9-133 * 

 arsenic J 



Tliese are the only hydrates (not reckoning the salts and 

 vegetable acids) at present known. It is evident, from the 

 slightest inspection of the table, how little they have been 

 examined, and how uncertain we still are respecting the propor- 

 tions of the constituents of several. They deserve a more 

 careful examination than has hitherto been bestowed upon them ; 

 and, if accurately understood, would greatly facilitate many im- 

 portant processes in practical chemistry. It is particularly 

 worthy of inquiry, whether all metallic oxides be capable of 

 forming hydrates, or only some of them. The former is the 

 more probable opinion ; but it is very far from being determined. 



composed of 95 • black oxide + 5 water. Now this approaches 

 to 1 particle of black oxide and 1 particle of water. 



* There can be no doubt that this hydrate exists ; but it has 

 not hitherto been analysed. I state its composition in the table 

 merely from analogy. 



y This is the green coloured substance obtained by dissolving 

 nickel in nitric acid, and precipitating by potash. According to 

 Davy, more than one-fourth of its weight is water. This state- 

 ment approaches most nearly to the supposition that it contains 

 2 particles of water to 1 of oxide. 



This is the blue powder obtained by dissolving cobalt in an 

 acid, and precipitating by an alkali. It has not been analysed. 

 The number in the table is given merely from analog}'. 



:i This is the white powder precipitated by alkalies fromcolour- 

 Ir-is solutions of manganese. It has never been analysed. Hence 

 the numbers in the table are given only from analogy. 



'' This i i the opake white powder, or the small white crystals, 

 of oxide of arsenic. The pure oxide is transparent and colour- 



i, like glass. This hydrate has never been analysed. The 

 numbers in the table arc stated merely from analogy. . 



