RESEARCH FOR ARSENIC AND ANTIMONY. 
95 
There were other and manifest conveniences attending the use 
of this method. The arsenic not being converted to a gas 
and burnt, there was no loss of the poison ; it was entirely 
removed from the fluid in a state of pure metal, and the 
separation of it might be suspended and resumed at any sub¬ 
sequent period. Reinsch thought that his process was beyond 
the reach of any fallacy, because, when arsenic was really 
present in a liquid, even in small quantity, the deposit com¬ 
menced in a few minutes, and was completed in half an hour ; 
and during this time, if arsenic was not present, the copper 
would be still bright on its surface, and present no appearance 
which could give rise to any error.* The facts upon which 
the discoverer relied for the demonstration of the presence of 
arsenic were—1, the gray, metallic appearance of the deposit; 
2, the conversion of this deposit by a moderate heat to a 
crystalline sublimate of arsenious acid, in which the octahe¬ 
dral form of the crystals would be recognisable; 3, the 
solubility of these crystals in water, and the results of the 
application of the liquid reagents for arsenic to the solution. 
The only important addition which has been since made to 
these corroborative tests consists in the conversion of a sub¬ 
limate of the crystals to arsenious acid by nitric acid, and the 
production of red arseniate of silver on the addition of a 
solution of nitrate of silver to the dry residue. 
With the above-mentioned results, Reinsch pronounced his 
process to be entirely free from any fallacy, or from any pos¬ 
sibility of error. He also thought that there could be no loss 
of arsenic. He asserted that it was the most delicate of all 
the processes hitherto contrived for the detection of this 
poison, and that it would reveal its presence even when it 
formed only the 1-200,000th part of the solution. This 
remark obviously applies to the mere effects of dilution. The 
actual weight of arsenic which can be detected in a minimum 
quantity of water is not assigned by Reinsch. 
Most analysts who have had occasion to employ this 
process can corroborate the statement of the discoverer, to 
the effect that it is simple, delicate, and easy of application. 
In regard to its delicacy—if the deposition of a metallic film 
on copper is taken as a criterion, I can state, from direct 
experiment, that the l-4000th part of a grain of arsenious 
acid admits of detection. This small quantity of arsenic, 
dissolved in a minim of water and mixed with ten minims of 
* ‘ Annales d’Hygiene, 5 1843, i, 449. This view is not strictly correct: 
small quantities of arsenic or antimony contained in large quantities of 
organic matter require some hours’ boiling for their entire separation and 
deposition. 
