324 
Journal of Agricultural Research 
Vol. XXV, No. 7 
H 2 0 ? . The originators of this method stated that the number of cubic 
centimeters of HC 1 used is the amount necessary to react with both the 
polysulphid and the hydroxid present, the solution always being alkaline 
due to the hydrolysis of the polysulphid. 
Chapin (j, 4) originated new methods for the determination, iodo- 
metrically, of the three principal forms of sulphur, monosulphid poly¬ 
sulphid, and thiosulphate, the latter being the compound directly 
titrated in each case. His methods were based, and adjusted accordingly, 
on solutions containing 1.5 to 2 per cent of sulphid sulphur. Chapin 
stated that increasing the quantity of sample and using stronger solutions 
for titrations might very likely improve the accuracy in some of the 
results. 
Harris (5) determined both the monosulphid and thiosulphate sulphur 
in diluted solutions by a double iodin titration. The amount of N/10 
iodin required to destroy the yellow color of the soluble sulphids was the 
monosulphid sulphur equivalent. The thiosulphate sulphur was de¬ 
termined by continuing the addition of iodin after the monosulphid 
end-point had been reached, with starch as indicator. The total sulphur 
was determined by oxidizing the sulphur in solution with Na^. 
Averitt (/) estimated the monosulphid sulphur by titrating a dilute 
solution with N/10 HC 1 , using in one case either methyl orange or methyl 
red as an indicator, and in another case sodium nitroprussid as an inside 
indicator. The thiosulphate sulphur was determined, when either of 
the first two indicators was used, by titrating with iodin the diluted 
filtrate, with or without starch, after boiling off the H 2 S in solution. 
When sodium nitroprussid was employed, the thiosulphate sulphur was 
determined by a further addition of iodin until a faint coloration was 
produced. 
RELATION OF FOREGOING METHODS TO THE CHEMISTRY OF 
LIME-SULPHUR 
When dry lime-sulphur mixtures are subjected to analysis, it is the 
opinion of the writer that it is entirely unnecessary and erroneous to 
make a solution of high concentration and then to base quantitative 
results upon a diluted portion of the highly concentrated solution. 
The writer believes that the weak compounds contained in dry lime- 
sulphur when dissolved in water exist in a complex state of equilibrium 
so very susceptible even to slight outside influences that these disturbing 
factors will seriously affect the percentage composition of the constituents 
if the analysis is based on a diluted solution. It is a well-known fact that 
polysulphids in aqueous solutions are hydrolyzed to a greater or less 
degree, depending upon the concentration, and to some extent upon the 
temperature, of the solution. The hydrolysis of calcium polysulphid 
might be represented by the following equation: 
2 CaS. Sx + 2 H 3 0 = Ca (OH) 2 -f-Ca (SH) 2 -f-2 S x . 
The amount of sulphur deposited is of course dependent upon the 
concentration of the Ca (OH) 2 . 
The two points mentioned, (a) the action of external factors such as 
carbon dioxid and oxygen of the atmosphere, and ( b ) the resulting 
differences in the amount of sulphur in solution due to hydrolysis, should 
control to a large extent the preparation of the sample and the methods 
to be applied for the determination of the desired constituents contained 
in dry lime-sulphur mixtures. 
