SAMPLING AND TESTING HIGHWAY MATERIALS. 29 
used where the (•(instruction of the bin permits. Samples shall 
be taken from points well distributed over the face of the bin. 
(c) From filled Mns at points of discharge. — Sufficient ce- 
ment shall be drawn from the discharge openings to obtain 
samples representative of the cement contained in the bin, as 
determined by the appearance at the discharge openings of indi- 
cators placed on the surface of the cement directly above these 
openings before drawing of the cement is started. 
19. Samples preferably shall be shipped and stored in air- 
tight containers. Samples shall be passed through a sieve having 
20 meshes per linear inch in order to mix the sample thoroughly, 
break up lumps, and remove foreign materials, 
VII. CHEMICAL ANALYSIS. 
Loss ox Ignition. 
20. One gram of cement shall be heated in a weighed covered Loss on 
platinum crucible, of 20 to 25 cubic centimeters capacity, as fol- ignition. 
lows, using either method (a) or (&) as ordered: 
(a) The crucible shall be placed in a hole in an asbestos board, 
clamped horizontally so that about three-fifths of the crucible 
projects below, and blasted at a full red heat for 15 minutes with 
an inclined flame ; the loss in weight shall be checked by a second 
blasting for 5 minutes. Care shall be taken to wipe off particles 
of asbestos that may adhere to the crucible when withdrawn from 
the hole in the board. Greater neatness and shortening of the 
time of heating are secured by making a hole to fit the crucible in 
a circular disk of sheet platinum and placing* this disk over a 
somewhat larger hole in an asbestos board. 
(&) The crucible shall be placed in a muffle at any temperature 
between 900° and 1,000° C. for 15 minutes and the loss in weight 
shall be checked by a second heating for 5 minutes. 
21. A permissible variation of 0.25 will be allowed, and all re- 
sults in excess of the specified limit but within this permissible 
variation shall be reported as 4 per cent. 
Insoluble Residue. 
22. To a 1-gram sample of cement shall be added 10 cubic Insoluble 
centimeters of water and 5 cubic centimeters of concentrated residue. 
hydrochloric acid; the liquid shall be warmed until effervescence 
ceases. The solution shall be diluted to 50 cubic centimeters and 
digested on a steam bath or hot plate until it is evident that de- 
composition of the cement is complete. The residue shall be fil- 
tered, washed with cold water, and the filter paper and contents 
digested in about 30 cubic centimeters of a 5 per cent solution of 
sodium carbonate, the liquid being held at a temperature just 
short of boiling for 15 minutes. The remaining residue shall 
be filtered, washed with cold water, then with a few drops of 
hot hydrochloric acid, 1 : 9, and finally with hot water, and then 
ignited at a red heat and weighed as the insoluble residue. 
23. A permissible variation of 0.15 will be allowed, and all re- 
sults in excess of the specified limit but within this permissible 
variation shall be reported as 0.85 per cent. 
Sulphuric Anhydride. 
24. One gram of the cement shall be dissolved in 5 cubic centi- Sulphuric 
meters of concentrated hydrochloric acid diluted with 5 cubic anhydride. 
centimeters of water, with gentle warming; when solution is 
complete, 40 cubic centimeters of water shall be added, the solu- 
tion filtered, and the residue washed thoroughly with water. 
The solution shall be diluted to 250 cubic centimeters, heated to 
boiling, and 10 cubic centimeters of a hot 10 per cent solution 
of barium chloride shall be added slowly, drop by drop, from a 
