<278 Notices respecting New Books. 



a bland taste like milk, but in a few minutes excited a sense of 

 roughness (aprett), and soon after the usual effects of burning." 



We need not stop to describe Dr. Christison's method of de- 

 tecting the presence of arsenic, as his views are already before the 

 public. On the odour of arsenic, as a test, we may, however, ex- 

 tract the following comment. " This test should be altogether dis- 

 carded. It does not always detect arsenic when present ; and the 

 alliaceous odour is not an infallible proof that it is present. Zinc 

 powder projected on burning fuel emits the same odour. Phos- 

 phorus, phosphoric acid, and the phosphates give out a similar 

 odour ; and I have frequently remarked one very like it from burn- 

 ing paper. What is of more consequence, however, a very small 

 portion of vegetable or animal matter, present in the matter sub- 

 jected to trial, obscures the alliaceous smell entirely. This I have 

 often observed, and the same thing was stated long ago by Pyl and 

 Hahnemann. If any one should nevertheless wish to have re- 

 course to this test, the proper way to try it, is to breathe gently 

 with the nostrils into the tube immediately after the metal has been 

 sublimed, and then to smell it." 



In speaking of the detection of arsenic by means of the ara- 

 moniacal nitrate of silver, and of the obscurity occasioned by the 

 presence of sea-salt, the following simple method is given for 

 avoiding uncertainty arising from this source. " The best way of 

 getting rid of this difficulty is to use in the first instance, not the 

 ammoniacal nitrate, but the nitrate of silver as long as any white 

 precipitate falls down, to add a slight excess of that test, and then, 

 after subsidence, to drop in ammonia. No arsenic is thrown down 

 by the first steps of this process ; but if any be present, it is thrown 

 down in the form of the rich yellow arsenite of silver, on the sub- 

 sequent addition of ammonia. This very simple mode of getting 

 rid of the chloride of sodium has been lately suggested by Dr. 

 Forbes, Professor of Chemistry, Aberdeen." The same principle 

 has been since applied by Dr. Christison, for removing animal sub- 

 stances, as preparatory to the precipitation of arsenic by sulphu- 

 retted hydrogen ; a preparation which should never be omitted 

 when much animal matter is present, as it is very apt to adhere to 

 the sulphuret of arsenic, and prove troublesome in the process of 

 reduction. This difficulty is avoided by adding nitrate of silver as 

 long as any precipitate falls, when all the animal matter is thrown 

 down in combination with oxide of silver, and arsenious acid re- 

 mains in solution, provided care is taken that no uncombined alkali 

 is present. The excess of silver is subsequently removed by mu- 

 riate of soda, and the arsenic thrown down as usual by sulphuretted 

 hydrogen. It is important, however, to neutralize the free nitric 

 acid before transmitting sulphuretted hydrogen gas through the li- 

 quid ; since otherwise the sulphuret of arsenic would be mixed 

 with free sulphur, the presence of which renders the reduction by 

 black flux both difficult and uncertain. 



As the action of water on orpiment is important and not ge- 

 nerally noticed in systematic works on chemistry, we extract the 



following 



