280 VETEEINAKY TOXICOLOGY 



valuable application from German forensic chemists than it 

 has received in this country. It is a very good method, 

 capable of numerous applications — e.g., to lead precipitated 

 as iodide, to barium as sulphate or chromate, to silver as 

 chloride or iodide, to tin as dioxide, etc. , 



In the determination of traces of arsenic the size and 

 intensity of the mirror obtained in Marsh's test are compared 

 with those given by known quantities of arsenic and formed 

 under experimental conditions as nearly alike as possible. 



GROUP A. 



The separation of volatile poisons depends on the fact 

 that they are more or less readily gasified and distilled 

 along with steam from a boiling paste of the materials with 

 water. In practice, distillation in steam is preferable to 

 ordinary distillation, because the boiling is more regular, 

 and the operation does not require so much attention. It 

 is advisable to place the distilling flask in a boiling water 

 bath, and to regulate the steam current, so that the quantity 

 of boiling fluid remains about constant. In this way dis- 

 tillation may be allowed to proceed to any desired extent. 

 For details of the process of distillation reference may be 

 made to a textbook of practical chemistry. 



The best method of procedure is to make a thin paste of 

 the material, and ascertain its reaction (acid, alkaline, or 

 neutral), if necessary acidify with either tartaric or dilute 

 sulphuric acid, and distil in a current of steam. Volatile 

 substances separated from an acid solution include — 

 phosphorus, hydrocyanic acid, phenols, turpentine, savin, 

 essential oils, alcohol, ether, chloroform, chloral, sulphur- 

 etted hydrogen, and sulphur dioxide. 



The smell is characteristic (that of chloral in traces is 

 faint), but, unless the substance is present in relatively 

 large amount, it is masked more or less completely by the 

 natural smell of the ingesta or organs. Distinct flakes 

 (possibly of fatty acids) always pass over, and it is therefore 



