76 Remarks upon Arsenic. 



pear. The matter 'enters first into solution^ and then becomes 

 carbonized during the concentration of the hquid, which we con- 

 tinue to evaporate, stirring at the same time with a glass rod. 

 The carbonization takes place without any swelling up of the 

 materials, (as is the case when nitric acid is used.) The action 

 of the heat is prolonged until the carbon appears friable and al- 

 most dry. The capsule is now left to cool, and then there is 

 added to the carbon about the same quantity of nitric acid as we 

 did of sulphuric acid in the first part of the operation. This 

 serves to convert the arsenious into arsenic acid, which latter is 

 much more soluble than the former : we again evaporate to dry- 

 ness, and treat the residue with boiling water, which dissolves 

 the arsenic acid only, and is always perfectly limpid, and some- 

 times colorless ; and this liquid also, when introduced into Marsh's 

 apparatus, produces no froth." 



" This process is much preferable to the carbonization by nitric 

 acid, for we can more easily manage the operation, and a much 

 less quantity of reactives is required, (an important consideration,) 

 and there never is any deflagration." 



MM. Danger and Flandin recommend the use of a much small- 

 er quantity of nitric acid than has been stated, but from the pro- 

 duction very often of phosphite and sulphite of ammonia during 

 the action of the sulphuric acid upon the animal matter, it is ve- 

 ry necessary that there should be sufficient nitric acid to convert 

 these compounds into phosphate and sulphate of ammonia, for 

 otherwise our experiments would be singularly confused, as will 

 be shown a little farther on. It would appear that the arsenious 

 acid in the operation just stated, would be evaporated along with 

 the sulphuric acid, but some experiments performed by the com- 

 mittee before mentioned, with reference to that point, show that 

 no danger need be apprehended on that score. 



I have now stated the best method to pursue, in obtaining a 

 liquid that may contain all the arsenic in combination with any 

 organic matter, and also one that is proper to be introduced into 

 Marsh's apparatus. The next question that most naturally arises 

 is, what form of this apparatus is the one that is most calculated 

 to give us accurate results ? The committee of the Academy of 

 Sciences have also occupied themselves with this question, and 

 the following is a detailed account of the instrument that has 

 received their approval. 



