182 A. B. MACALLUM. 
During the last two years the dilute reagent has, in conse- 
quence of these facts, been exclusively employed. 
The glycerine used was chemically pure.! It gave the best 
results when diluted with an equal volume of distilled water. 
In making the preparations, the cellular elements were teased 
out on the slide in a drop of the dilute glycerine, and over this, 
after thorough admixture with two drops of the dilute solution 
of ammonium hydrogen sulphide, a cover-glass of 16—22 mm, 
square was placed. The teasing-out process was done in each 
case with a clean pair of goose-quill points. Every care was 
taken to prevent the occurrence of impurities in the prepara- 
tions. The excess of the glycerine and sulphide mixture is at 
first uncovered, but if the slide be put in a warm oven with a 
temperature of 60° C., the mixture rapidly concentrates and in 
a few minutes is wholly under the cover-glass. When the 
solution of ammonium hydrogen sulphide is deteriorated, a 
deposit of sulphur forms at the edges of the cover-glass and the 
mixture under the latter becomes yellow through the produc- 
tion of polysulphides ofammonium. Such preparations never 
yield anything of value. On the other hand, when the fluid 
under the cover-glass remains colourless and free sulphur does 
not form at the margins, the preparation, 1f kept at a tempera- 
ture of 55—60° C. for a period of from two to fifteen days, is 
almost always successful. Sometimes at the end of one, two, 
or three days the mixture is further concentrated and has 
receded from one edge of the cover-glass. This is remedied 
1 Molisch (‘Die Pflanze in ihren Beziehungen zum Nisen,’ p. 107) states 
that the glycerine of commerce—even the purest—contains traces of iron. I 
have not found this to be the case with Price’s glycerine, quantities of which, 
when mixed with ammonium hydrogen sulphide or diammonium sulphide, 
gave not the slightest reaction or precipitate, even after two weeks, and 
whenever portions of the stock supply used were evaporated at a low heat in 
a platinum dish no appreciable residue was left, and not a trace of iron or lead 
was detected. I found that in some samples of glycerine of other manufacture 
the sulphide gave no immediate reaction, but at the end of a week, or later, a 
small precipitate, composed partly of sulphide of iron, was at the bottom of 
the test-tube. A similar precipitate was obtained in portions of the stock 
supply of Price’s glycerine only when traces of an iron salt were added. 
