312 BOTANICAL GAZETTE [NOVEMBER 
One great advantage of the proposed method is that only two 
or three drops of sap are required for the determination. A film of 
sap is placed upon the prism, the prism is closed, and as soon as the . 
thermometer inclosed within the prism has reached 20° C. the read- 
ing of the moisture content can be made. The entire procedure 
need not take more than two minutes. 
The column “Moisture by refractometer” is read direct from 
the scale of the instrument, the next column was obtained by weigh- 
ing 10-20 gm. of the sap into a glass weighing bottle, and drying 
to constant weight at room temperature in a vacuum desiccator 
over sulphuric acid. The dried residue varied in color from a clear 
green to light brown, and still retained the characteristic odor of 
plant sap. 
The next two columns were obtained by heating the residues 
from the sulphuric acid vacuum treatment in a Freas vacuum oven 
at 100° under a vacuum of 28 inches for the stated period of time, 
and again weighing. It will be noted that in each instance there 
is a higher moisture content indicated by the further drying in the 
vacuum oven. We believe this to be almost entirely due to the 
decomposition of carbohydrates, since there was always marked 
browning or blackening of the residue, and a pronounced burned 
sugar odor. In no instance was the residue again wholly water 
soluble, and in every instance the water extracts of the residue 
were dark opaque brown, with a =— ee Clo: Further 
proof that this loss of weight is due to drates 
is afforded by the fact that the loss in weight continues for a long 
time, and constant weight is in many instances not reached even 
after seventy-two hours’ drying in the vacuum oven at 100° C. 
It will likewise be noted that in most instances the refracto- 
meter indicates slightly more total solids (that is, less water) than 
does the drying over sulphuric acid in vacwo. In every instance the 
sulphuric acid in the vacuum desiccator darkened as the drying 
progressed, indicating that volatile organic were dissolv 
ing in the sulphuric acid. It is self evident that esters, alcohols, 
ethers, and volatile oils are present in all plant saps, and none of 
these would be estimated by any drying method. We believe, 
therefore, that at least a part of the excess total solids indicated by 
the new method are due to such volatile compounds, and that the 
