366 Intelligence and Miscellaneous Articles. 



stannate of potash in solution. According to BerthoUet, jun., the 

 solution yields anhydrous protoxide of tin by evaporation. 



M. Fremy states that anhydrous oxide of tin is not soluble in a 

 weak solution of potash ; and whenever the hydrate in solution can 

 be deprived of its water, it quits the alkali and is precipitated ; this 

 curious property induced the author to examine the circumstances 

 under which protoxide of tin can be dehydrated. 



In the first place, it was found that the hydrate may lose its water 

 in a solution of potash ; if the hydrate be boiled in a very dilute so- 

 lution of the alkali, it is in a very few minutes converted into small 

 brilliant black crystals of anhydrous oxide of tin ; the influence of 

 the alkali in dehydrating the oxide is evident, for when equal quan- 

 tities of hydrated protoxide of tin are boiled, one in pure and the 

 other in alkaline water, the latter is very rapidly dehydrated ; on the 

 contrary, it requires a very long time to dehydrate the oxide in pure 

 water. 



Heat is not indispensable to cause an alkali to dehydrate oxide of 

 tin ; for if a solution of potash and hydrate of tin be put under the 

 receiver of the air-pump, the oxide becomes anhydrous as soon as 

 the potash is sufficiently concentrated. 



These experiments explain the decomposition which a solution of 

 oxide of tin in potash undergoes ; this solution cannot be made 

 without an excess of alkali, and as long as the solution is weak the 

 oxide remains dissolved ; but when the liquor is concentrated, the 

 oxide is dehydrated, and precipitates in that state. On this account 

 it is impossible to evaporate, even in vacuo, a solution of protoxide 

 of tin in potash, without observing that at a certain point of the 

 concentration the liquor deposits anhydrous oxide of tin. These 

 facts agree with those observed by BerthoUet, jun. ; tl;iey show that 

 protoxide of tin dissolved in a dilute solution of potash may be de- 

 hydrated and precipitated anhydrous. 



In order to repeat Proust's experiment, protoxide of tin was dis- 

 solved in potash, and instead of evaporating the solution slowly, as 

 in the preceding case, it was submitted to rapid evaporation ; the 

 protoxide of tin was then decomposed, the liquor deposited metallic 

 tin and held stannate of potash in solution ; it is therefore evident 

 that the products of the decomposition vary wiUi the concentration 

 of the alkali ; when the liquor is dilute and weakly alkaline, anhy- 

 drous protoxide of tin is precipitated, and it is only when the alkali 

 is concentrated, that the i)rotoxide is converted into tin and stannic 

 acid. 



These experiments show that dehydration takes place more readily 

 in a hot solution of potash than a cold one. Must it then be ad- 

 mitted that a solution of potash, even when dilute, has an affinity 

 for water and can take it from an hydrated oxide } or may not these 

 effects be explained by the interesting experiments of M. Mitscher- 

 lich on aetherification, which prove that a certain quantity of sul- 

 phuric acid may convert alcohol into aether almost indefinitely ? The 

 author thinks it is difficult at present to explain the fact in a satis- 

 factory manner; but he found that solution of sulphate of soda. 



