Chemical Science. S03 



Increased ad Hhitum, particularly in the case of Hme water. The 

 cause of the precipitate appears to be the same in all these cases. 

 The moment a drop of the solution is converted into vapour, it de- 

 posits the quantity of lime or salt which it held in solution ; and in 

 the case of bodies which dissolve so sparingly and with so much 

 difficulty, althouj^h the water be returned again to the solution, it 

 is incapable of re-dissolving what it has deposited. We know that 

 it would be a hopeless task to form a saturated solution of lime by 

 agitating with the water no more than the few grains which it is 

 capable of dissolving ; and in the case of ebullition, when the lime 

 is once deposited, there should be the same difficulty in taking it up. 

 ' Mr. Graham states that he has observed this effect not only in 

 lime-water and in solution of phosphate of magnesia, but to a cer- 

 tain extent in all bodies of difficult solubility, in the sulphate of 

 lime, for instance, even when greatly diluted; and he believes that 

 the deposite from slight boiling observed in many mineral waters, 

 and generally attributed to the dissipation of carbonic acid gas, 

 depends, in some instances, upon this cause. However weak the 

 solution may be, it is evident that a portion of the salt may be de- 

 posited in this way. 



7. On the Composition of Cyanic Acid. — M . Wohler some time 

 since announced the production of cyanic acid, and cyanates, corre- 

 sponding in composition to the substance presumed to exist in the 

 fulminating compounds of silver, mercury, &c., the nature of which 

 was made out by MM. Liebig and Gay Lussac. M. Liebig, upon 

 repeating M. Wohler's experiments upon his cyanate of silver, ob- 

 tained only 71.012 per cent, of oxide of silver, instead of 77.23, 

 which was the quantity present according to M. Wohler's analysis, 

 and Concluded that the acid was the cyanous, and not the cyanic. 

 The latter philosopher was consequently induced to repeat his ex- 

 periments: one of his methods of decomposing the cyanate of silver 

 was by muriatic acid gas : at first liquid cyanic acid forms, which is 

 very soon transformed into a white crystalline mass ; but, on con- 

 tinuing the operation, and applying a higher heat, a large quantity 

 of muriate of ammonia and cyanic acid is evolved. This process 

 indicated 77.5 per cent, of oxide of silver in the salt. Another 

 process consisted in dissolving the cyanate in nitric acid, and pre- 

 cipitating the silver by muriatic acid, the result was 77.05 of oxide 

 per cent. A third analysis, made by reducing the silver of the salt, 

 gave a result of 77.35 per cent, oxide. The mean of these is 77.3, 

 and the theoretical number obtained by calculation is 77.23, so 

 that the acid appears to be truly the cyanic ; and the curious fact of 

 its being the same in composition with that in the fulminating com- 

 pounds of silver and mercury, but very unlike in properties, still 

 remains undisturbed. — Bull. Univ.y A. viii. 53. 



8. lodous AQid.—'A.ccordmg to M. Wohler, the iodous acid of 



