Intelligence and Miscellaneous Articles. 381 



in the alkalies, and which may be considered as weak acids. It was 

 found that these bodies possess the property of combining with bases 

 iu the state of hydrates only. Thus, hydrated binoxide of copper 

 dried in the air, the formula of which is Cu O- HO, is perfectly 

 soluble in excess of potash and soda ; the solutioia is of a fine blue 

 colour, and when evaporated, even in vacuo, it is decomposed, and 

 deposits oxide of copper, which is insoluble in the alkalies. The 

 hydrates of oxides of tin, antimony and chromium, SnO, HO ; 

 Sb 03, HO ; Cr'^ O^ lOHO, dissolve in the alkalies, and all become 

 insoluble by losing water. The author satisfied himself that the in- 

 solubility was owing to the separation of the water, and not to the 

 isomeric modifications which certain oxides undergo by calcination. 



It was found impossible to obtain crystalline compounds of the 

 above-mentioned hydrates with the alkalies ; for by evaporation, 

 even in vacuo, the alkali which it is requisite to employ in excess 

 combines with the water of the hydrates, or in acting perhaps only 

 by its presence occasions the precipitation of the anhydrous oxide. 



The preceding compounds yield, however, incontestable proof of 

 the existence of saline groups, which are not possible without the 

 presence of water : they demonstrate that certain hydrates owe their 

 solubility in the allialies entirely to water of hydration. 



The new facts stated establish marked differences between stannic 

 acid and the acid which M. Fremy calls metasiannic acid; and this 

 he has found forms three different hydrates with water : the first is 

 insoluble in nitric acid and soluble in ammonia ; it is obtained by 

 precipitating a metastannate by an acid ; the second is produced by 

 the reaction of nitric acid upon tin ; its formula is Sn* O''', lOHO ; 

 it is insoluble in ammonia and nitric acid ; the third is prepared by 

 drying the preceding hydrate at 266° F. ; its formula is Sn* 0'°, 

 4H0. 



Neutral metastannates, formed in the presence of great excess of 

 alkali, have for their formula Sn' 0'°, MO, 4H0, whereas stannates 

 are represented by Sn O" MO. The equivalent of metastannic acid 

 is then five times greater than that of stannic acid. The metastan- 

 nates are always hydrated, are necessarily ternary, and decompose 

 when dehydrated : in this case the metastannic acid loses its acidity, 

 whereas stannates, like most other salts, may be rendered anhydrous 

 without decomposing. 



The essential action of water on the constitution of the metastan- 

 nates, may be readily shown by the following experiments. If me- 

 tastannate of potash be gently heated, so as to take away its water 

 of combination, the separation of the acid and base is immediately 

 effected : on treating the dehydrated salt with water, potash only is 

 dissolved, which does not contain a trace of metastannic acid, and 

 this acid remains in an insoluble state. In tliis case, therefore, a 

 decomposition is effected upon a definite salt, similar to that which 

 the binoxide of copper undergoes in potash when heated : these two 

 phenomena are precisely of the same descrijjtion. 



The dehydration of metastannate of soda is perhaps still more 

 remarkable, for it takes place below 21 2° F, 'I'his salt is soluble in 



