Langenhaii—-The Arsenical Solutions. 
183 
taining iodeosin and eosin, the former being tetra-iodo-fluorescein, 
and the latter a tetra-brom-fluorescein. Tubes 2, 3, and 4 of these 
series developed an intense yellow fluorescene when viewed by re¬ 
flected light, which was not evident in the remaining tubes. 
A third series worth mentioning is the one that contains alkali 
blue. In this series tubes 3 and 5 have the same color which dif¬ 
fers from that of any of the remaining four. These tubes viz. 3 
and 5, contained 
As(OH)3 + 2KOH , and KOH 
5 5 5 
respectively. Whether one may assume that one molecule of potas¬ 
sium hydroxide is uncombined in each tube, leaving one molecule 
combined with the As (OH) 3 in the first tube is possibly open to 
question. Yet the sameness of color of these two tubes was so 
striking that the fact seemed worth mentioning. 
15.) Assay. From 1880 on the U. S. P. gives directions for the 
assay of Fowler’s Solution. The quantitative determination of 
trivalent arsenic as As 2 0 3 is not only a check on the amount of 
arsenic trioxide employed, but also on the possible deterioration 
of the solution, brought about by the oxidation of the arsenite to 
arsenate, in the presence of water, as expressed by the following 
reactions:— 
H 2 0 + I 2 =2HI+ O 
As 3 0 3 + 20 = As 2 0 5 , or 
AsO.OK + O = AsO a OK , or 
As(OH) 2 OK + O = AsO(OH) 2 OK, hence 
1 4 equiv. 0 2 equiv. As s 0 3 , 
126.92 equiv. 197.92 Qr 
0.012692 equiv. 0.004948 
The amount of As 2 0 3 as determined by the prescribed volumetric 
assay varies to a slight degree. The U. S. P. of 1880, the first to 
introduce an assay method, states that 24.7 gm. of the solution 
“should require from 48.5 to 50 cc. of volumetric solution of 
iodine”—(“corresponding to 1 per cent, of arsenious acid of the 
required purity”.) The As 2 0 3 equivalents of 48.5 and 50 cc. re¬ 
spectively of N/10 I. Y. S. are 0.9709 gm. and 1.001 gm. As the 
purity rubric for “arsenious acid” was “at least 97 per cent. 
