—— 2°? ——~ « eee 
_ o> 8 
EE 
tats =~ ae 
a ee 
Se Bioe 
—-. 
» 
Soe eee 
ee ~ 
$e 
Pe tee le ea 
ae aes 
—t, 
Acid by Hydrochloric Acid. 401 
To determine in a general way the point of dilution at 
which mixtures of selenic and hydrochloric acids yield chlorine, 
we submitted various mixtures to distillation in a retort 
arranged with an inverted condenser (so that the aqueous dis. 
tillate might be constantly returned to the retort) which was 
joined to an absorbtion apparatus charged with a solution of 
potassium iodide. A current of carbon dioxide was passed 
through the apparatus during the distillation, to carry forward 
whatever chlorine might be evolved in the process. The 
iodine liberated in the absorbtion apparatus was determined by 
titration with standard sodium thiosulphate. The results of 
these experiments are given in the accompanying table. 
Percent of HCl, Chlorine in 
SeO; present. Total volume. sp. er. 1°20, by Time in terms of the 
grm. cm? volume. minutes. theoretical total. 
0°1144 100 5 ; 5 None 
ee se 10 a None 
“sé s 15 te About 1% 
6¢ ce 20 6¢ 66 7% 
66 6¢ 95 6c 66 30% 
ec 6G 30 74 44 70% 
/ 
It is plain that so long as the volume of the hydrochloric 
acid, sp. gr. 1:20, does not amount to more than ten per cent 
of the entire liquid no chlorine whatever is evolved, and that 
only when the percentage of this acid rises as high as thirty 
does the chlorine evolved during boiling for five minutes 
_ approach the theoretical yield. In the ordinary process of dis- 
tillation, in which the inverted condenser is not used, the 
liquid must gradually concentrate and the acid become stronger, 
so that under such conditions the yield of chlorine in a defi- 
nite period of time must generally be greater than that ob- 
tained in the corresponding experiments of the table. Obvi- 
ously it is advantageous, in attempting the practical reduction 
of selenic acid, to begin the distillation with acid of strength 
sufficient to insure the evolution of chlorine in quantity at the 
outset, and we have found it best to start with a mixture one- 
third of which is the strongest aqueous hydrochloric acid, sp. 
gr. 1:20. With solutions so constituted the reduction goes on 
rapidly. We have found, however, that care must be taken 
not to prolong the boiling after the solution reaches a concen- 
tration corresponding to hydrochloric acid of half-strength ; 
for under such conditions—attained in our experiments either 
by boiling down mixtures of selenious acid and hydrochloric 
acid, or by making mixtures of selenious acid containing 
hydrochloric acid of half-strength—we have found that 
selenium appears visibly in the distillate, while iodine is set 
free from the iodide in the receiver. Good results may be 
