576 
Journal of Agricultural Research 
Vol. XXI, No. 8 
recommendations have been made that the solution be discarded after 
3 or 4 bushels of sweet potatoes were treated. Harter 1 states that the 
solution should not be used more than two or, three times, since it loses 
its efficiency by repeated use. On the other hand, Taubenhaus 2 advises 
that the solution be used until exhausted. 
The experiments reported in this paper were designed (i) to deter¬ 
mine the rate of reduction in the strength of the mercuric-chlorid solu¬ 
tion used for treating sweet potatoes and (2) to work out a method of 
procedure for growers whereby they might be reasonably sure of main¬ 
taining the solution at approximately its original strength with the 
least expenditure of time and money. 
METHODS 
The sweet potatoes used in these experiments were of the Yellow 
Jersey variety, grown on a sandy soil and stored in crates. The potatoes 
were sorted and placed in bushel hampers in which they were treated. 
In this manner the amount of dirt added to the solution was reduced 
to a minimum—that actually clinging to the potatoes. The solution 
was made up in a clean 50-gallon oak barrel by adding 4 ounces of mer¬ 
curic chlorid previously dissolved in warm water to 32 gallons of water. 
Samples of the solution were taken for analysis both before being used 
and from time to time as indicated in the tables. I11 order to keep the 
solution as nearly as possible at its original strength, ^ ounce of mercuric 
chlorid was added after each 10 bushels of potatoes were treated. In the 
experiments where the amount of mercuric chlorid removed by a specific 
substance, such as dirt, bags, hamper, etc., was being tested, the receptacle 
used for the solution was of such a nature that no reaction would take 
place between it and the chemical. In all such experiments, except 
where the hamper and the 30 pounds of potatoes were treated, a 2K“ 
gallon porcelain bucket containing 2 gallons of solution was used, and in 
those two cases a io-gallon glazed earthen jar with 7 gallons of solution 
was used. 
The samples were analyzed the same day the treatments were made, 
with the exception of those in the experiments, the results of which are 
recorded in Table I. These were made the following day. All analyses 
were made by the volumetric method described by Jamieson. 3 In brief, 
the method consists of precipitating the mercury as mercury zinc thio¬ 
cyanate, collecting the precipitate on a filter, and titrating it with a 
standard solution of potassium iodate (KI 0 3 ) in the presence of strong 
hydrochloric acid, using chloroform as an indicator. 
1 Harter, E. E. sweet potato diseases. U. S. Dept. Agr. Farmers’ Bui. 714, 26 p. t 21 fig. 1016. 
2 Taubenhaus, J. J. field diseases of the sweet potato in Texas. Tex. Agr. Exp. Sta. Bui. 249, 
2a p.,34 fig. 1919. 
8 Jamieson, George S. the gravimetric and volumetric determination of mercury precifi- 
TATEd as MERCURY zinc thiocyanate, Jn Jour. Indus. Eugin. Chem., V. II, no. 4, p. 296-297. 1919 
