July 15, 1921 
Reduction Strength of Mercuric-Chlorid Solution 
577 
Duplicate samples of 100 cc. each were placed in clean 250-cc. beakers, 
to which were added 25 cc. of the precipitating reagent, which consists 
of 39 gm. of ammonium thiocyanate and 29 gm. of zinc sulphate per 
liter. The solutions were vibrated by striking the sides of the beakers 
with a stirring rod to facilitate the separation of the crystals. After 
five minutes they were stirred rapidly for one minute and then allowed to 
stand for one hour or longer. Each solution was then filtered through 
a No. 42, 9-cm., chemically prepared Whatman's filter paper by the aid 
of gentle suction. The filter paper and precipitate were washed thor¬ 
oughly with a solution made by adding 10 cc. of the thiocyanate reagent 
to 450 cc. of water. When the filter paper was thoroughly drained it was 
removed to a glass-stoppered titration bottle. To each bottle was then 
added a mixture consisting of 35 cc. of concentrated hydrochloric acid, 
10 cc. of water, and 7 cc. of chloroform. This solution was then imme¬ 
diately titrated against a standard potassium-iodate solution containing 
19.2191 gm. of potassium iodate per liter. The iodin liberated gave a 
brilliant red color to the chloroform, which changed to a pink and dis¬ 
appeared altogether when the end point was reached. The chloroform 
settled to the bottom of the bottle, and even in the presence of a con¬ 
siderable amount of dirt the end point was not obscured. Hence it 
was never necessary to filter the solutions to be tested. 
In previous years attempts were made to carry out experiments of a 
similar nature, using the potassium-cyanid method for the determina¬ 
tion of mercury. This method consists in titrating the mercuric-chlorid 
solution against a standard potassium-cyanid solution, using phenol- 
phthalein as an indicator. In order to detect the end point, it was nec¬ 
essary to have a clear, colorless solution, which was often impracticable, 
especially since every attempt made to clear the solutions resulted in a 
decrease in the amount of mercury. The strength of a clean, standard 
solution of mercuric chlorid filtered through a single filter paper of 
various grades was reduced 1 to 3 per cent, and when two filter papers 
were used the concentration was lessened by as much as 6 per cent. 
In view of these facts a method had to be found in which filtering was 
not necessary. In one instance an attempt was made to determine the 
amount of mercury removed by a gunny sack by the use of potassium 
cyanid, but the analysis showed a larger amount of mercuric chlorid 
present in the solution after soaking the sack for 10 minutes than at the 
start. These results indicate that some substance present in the sack 
reacted with the potassium cyanid. No such inconsistencies were found 
in any of the analyses made by the Jamieson method. Some variation 
in the duplicate titrations occurred, but this was never more than one- 
half of 1 per cent and was usually less. The figures given in the tables 
are calculated from the averages of two or more titrations. 
