on Impurity in Metallic Zine. 383 
_ 2. 200 grammes of Vieille Montagne zine, and about 200 ¢.c. of pu- 
tified sulphuric acid, were thoroughly tested, and gave no deposit in the 
terials as in the last experiment, we obtained in half an hour, a very large 
and distinct mirror of arsenic, by introducing into the flask one tenth of 
contents had been proved as above described, and at the end of three 
quarters of an hour a distinct deposit of arsenic was found in the reduc- 
tion-tube. ‘The amount of arsenious acid actually placed in the flask was 
two hundred-thousandths of a gramme (,00002 gram.). 
000002 grm. arsenious acid = 0°000015 grm. arsenic. 
Ratio of the arsenic present to the zine = 0°000015 : 200 = 50 00 00" 
© «@  «  @  ® amount of liquid in the flask = about 5 maa: 
Our apparatus was therefore competent to detect a uantity of arsenic 
less than one ten-millionth of the weight of the zinc used, or of the amount 
cesses, the comparative coarseness of t ; 
unavoidable inaccuracies in weighing and measuring, 1s not the assertion 
Perfectly safe, and in strict conformity with the general use of language 
in other qualitative or quantitative determinations, that a specimen of 
