466 
CHEMICAL ANALYSIS. 
lution containing organic matter, even although arsenious acid 
be absent. With reference to Mr. Harrison's remarks, justify¬ 
ing the employment of chloride of calcium, and a mixture of 
caustic potash and sulphate of copper as tests for arsenic,and 
to his observation respecting the addition of caustic potash to 
get over the iC little difficulty, 5 ' as he terms it, of obtaining a 
precipitate by ammonio-sulphate of copper, in a solution of 
arsenious acid, containing free hydrochloric acid, I need 
only repeat that which I stated in my last letter; viz., 
that the first two tests are valueless, even as corroborative 
ones, for arsenious acid, in consequence of the innume¬ 
rable sources of error to which they are subject; and that 
very much greater and more numerous precautions have to be 
observed in order to obtain a precipitate which can be sworn 
to as Scheele’s green, than apparently Mr. Harrison fancies 
to be necessary. 
As I do not wish Mr. Harrison to think that it is either 
pleasing or satisfactory to me to criticise his chemical know¬ 
ledge ; I may here observe that it would afford me the greatest 
pleasure if I could see veterinary surgeons practically applying 
for themselves that science which I have made my profession, 
and in the pursuit of which I find such inexhaustible sources 
of gratification and delight. 
Feeling that, as hitherto, I have done scarcely anything 
else than take objection to Mr. Harrison’s mode of con¬ 
ducting his investigation for the discovery of arsenic, it will 
now, I think, be only fair for me to conclude this letter by 
giving an outline of the most reliable processes employed 
by the most eminent toxicologists of the present day for the 
detection of that poison in an organ. 
Reinsch > s process .—Cut up the organs to be examined into 
small pieces; cover these with one part of strong hydro¬ 
chloric acid and two parts of distilled water, and boil the 
mixture until no more of the tissue can be dissolved. 
Strain the fluid thus produced through fine muslin, and 
boil it with strips of bright copper. Remove the strips of 
copper, now coated with an iron-gray deposit of metallic 
arsenic, from the fluid, dry them thoroughly, and heat them 
trongly in a German glass test-tube. A sublimate of arse¬ 
nious acid will form towards the upper, and upon the cool 
parts of the test-tube. This sublimate, when examined by 
the microscope, will be found to consist of a collection of 
octahedral crystals, or of forms derived from the octahedron. 
The crystalline sublimate of arsenious acid should be trans¬ 
ferred to a clean test-tube, boiled with distilled water, divided 
into four portions, and examined thus: 
