48 BULLETIN 898, U. S. DEPARTMENT OF AGRICULTURE. 
In the same way determine the percentage of H,SO, in the stock of ordinary con- 
centrated acid (sp. gr. 1.84). From these data calculate the quantity of the latter 
which must be added to the quantity of mixed acid in the weighed bottle to bring it 
to a concentration, in terms of H,SO,, of 100.92 per cent. 
After adjusting the concentration by the addition of the ordinary sulphuric acid, 
thoroughly shake the bottle of mixed acid and again determine its concentration. 
The allowable variation is + 0.05 per cent H,SO,. Finally as a check runa poly- 
merization test on gum turpentine known to be 
pure. The residue should fall below 2 per cent. 
Special precautions must be taken to prevent 
dilution of this acid by the absorption of atmos- 
pheric moisture. The arrangement shown in 
figure 7 is most suitable for storing and deliver- 
ing measured quantities of this reagent. 
- With the three-way stopcocks A and B in the 
position shown, acid is siphoned into the pipette 
P, the displaced air passing into R. Toempty 
the pipette, A and B are turned to the position 
shown by the broken lines, air passing in at a. 
The acid adhering to the walls of the pipette 
dries this air so that when it passes into R on 
again filling the pipette there is noaccumulation 
of moisture in the acid remaining in the reser- 
voir. Ifsuch arrangement is not to be had, the 
acid should be kept in well-fitting glass-stop- 
pered bottles of not more than one-half liter ca- 
pacity. 
5. BASIS OF PURCHASE. 
(a) Unit.—Turpentine shall be purchased (a) 
by volume, the unit being a gallon of 231 cubic 
inches at 15.5° C. (60° F.), or (6) by weight. A 
gallon of turpentine at 15.5° C. (60° F.) weighs 
7.19 to 7.30 pounds. The exact weight in 
pounds per gallon of any sample can be deter- 
mined by multiplying the specific gravity at 
15.5°/15.5° C. (60°/60° F.) by 8.33. Example 1: 
If the specific gravity at 15.5° C. is 0.8642, the 
weight per gallon at this temperature will be 
0.8642 X8.33=7.199 pounds. 
When purchased by weight, quotations shall 
be by the pound or by the 100 pounds. The re- 
quest for bids will state whether quotations shall be by the gallon, pound, or 100 
pounds. 
(b) Correction of volume.—The gallonage paid for shall be the volume corrected to 
a standard temperature of 15.5° C. (60° F.). The correction shall be deducted from 
(when the temperature of gaging is above 15.5° C.) or added to (when the temperature 
of gaging is below 15.5° ©.) the gallonage as gaged. Such deduction or addition shall 
Fic. 7.—Acid bottle and pipette. 
be computed on the basis of a coefficient of expansion for turpentine of 0.000945 per & © 
degree centigrade (or 0.000525 per degree Fahrenheit). Example 2: Ii the temperature 
at which the turpentine is gaged is 75° F. and the volume delivered (at that tem- 
perature) is 8,000 gallons, then 0.000525 15° X8,000 gallons equals the quantity in 
gallons which must be subtracted from 8,000 gallons to give the true gallonage at 
60° F., or, if the temperature at which the turpentine is gaged is 10° C., then 
