Chemical Science. 165 



their precipitation, and, consequently, these substances have existed 

 dissolved, in greater or smaller quantities, in the liquid from which the 

 minerals originated. 



" It results from my experiments, that the nitrate of barytes ought 

 to be proscribed our laboratories, as it gives results far more uncertain 

 than the muriate. It is the same with the nitrate of lead, which is 

 still more uncertain. M. Berzelius has frequently used it, particularly 

 in the analysis of vegetable acids, gum, starch, <§ - c. ; and I believe, 

 that notwithstanding the pains he has taken not to use nitrate of lead 

 in excess, he has not been able to obtain results without serious errors, 

 and that thus it is that the analyses of M. Berzelius differ frequently 

 from those made by other chemists. 



" The alkaline subcarbonates cannot be employed to estimate with 

 precision the quantity of lime dissolved by an acid in solution; and 

 the salts of lime cannot, in any circumstance, serve to estimate the 

 quantity of any alkaline subcarbonate in solution. 



" Finally, it results, that if by rigorors methods we succeed in 

 determining the proportions of the elements of salts, chemical analysis, 

 in general, would still not be more free from uncertainty ; for if, for ex- 

 ample, one perfect analysis of sulphate of barytes was made, it would 

 not be less true that a solution of muriate of barytes being poured 

 into any solution, to separate the sulphuric acid, the sulphate of ba- 

 rytes, which, by its weight, is to indicate the quantity of the acid, 

 having carried with it a certain portion of the elements, in contact 

 with which it was formed, would always give results, more or less 

 removed from the truth, since its weight would be complicated with 

 that of the impurity." — Ann. de Chim. xxiii. 241. 



11. Solubility diminished by heat. — If phosphate of iron be dissolved 

 in sulphuric acid, and the solution be diluted with some hundred times 

 its volume of water, a portion of the phosphate will be precipitated, 

 but some will remain in solution. On submitting this solution to 

 ebullition, some white flocculi of phosphate of iron will appear; on 

 cooling, the phosphate will be re-dissolved ; and these changes may be 

 repeated at pleasure. " It appears to me," says M. Longchamp, 

 " that this result can only be explained by supposing that the sul- 

 phuric acid quits the phosphate it previously holds in solution, to go 

 to the water, and oppose its resolution into vapour; and that when by 

 fall of temperature the caloric exerts no further molecular disintegrat- 

 ing action, the acid goes again to the phosphate it had abandoned, 

 and dissolves it." 



u It is also by the action which liquid water exerts on that which is 

 vaporizing, that we may explain why lime and magnesia are moie 

 soluble in cold than in hot water."— Ann. de Chim. xxiii. 19*2. 



12. Inflammability of Ammoniacal Gas. — Professor Silliman ob- 

 lervcSj that if a large jar of ammoniacal gas be opened in the air. 



