4 DEPARTMENT BULLETIN 1216, U. S. DEPT. OF AGRICULTURE 
22. A permissible variation of 0.25 will be allowed, and all results in excess 
of the specified limit but within this permissible variation shall be reported as 
4 per cent. 
INSOLUBLE RESIDUE 
23. To a 1-gram sample of cement shall be kidded 25 cubic centimeters of 
water and 5 cubic centimeters of concentrated hydrochloric acid (speific gravity 
1.19). Material shall be ground with the flattened end of a glass rod until it is 
evident that the decomposition of the cement is complete. The solution shall 
then be diluted to 50 cubic centimeters and digested on a steam bath for 15 
minutes. The residue shall be filtered, washed with cold water, and the filter 
paper and contents digested in about 30 cubic centimeters of a 5 per cent solu- 
tion 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 
hot water, then with a few drops of hot hydrochloric acid (1:9), and finally 
viih hot water, then ignited at a red heat and weighed as the insoluble residue. 
24. A permissible variation of 0.15 will be allowed, and all results in excess 
of the specified limit but within this permissible variation shall be reported as 
0.85 per cent. 
SULPHURIC ANHYDRIDE 
25. To a 1-gram sample of cement shall be added 25 cubic centimeters of 
water and 5 cubic centimeters of concentrated hydrochloric acid (specific gravity, 
l.lil). Material shall be ground with the flattened end of glass rod until it is 
evident that decomposition of the cement is complete. The solution shall be 
diluted to 50 cubic centimeters and digested on a steam bath for 15 minutes, 
filtered, and the residue washed thoroughly with hot 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 pipette and the boiling continued until the precipitate is well 
formed. The solution shall then be digested on the steam bath at least three 
hours, preferably overnight. The precipitate shall be filtered, washed, and the 
paper and contents placed in a weighed platinum crucible and the paper slowly 
charred and consumed without flaming. The barium sulphate shall then be 
ignited and weighed. The weight obtained multiplied by 34.3 gives the per- 
centage of sulphuric anhydride. The acid filtrate obtained in the determination 
of the insoluble residue may be used for the estimation of sulphuric anhydride 
instead of using a separate sample. 
26. A permissible variation of 0.10 will be allowed, and all results in excess 
of the specified limit but within this permissible variation shall be reported as 
2.00 per cent. 
MAGNESIA 
27. To 0.5 gram of the cement in an evaporating dish shall be added 10 cubic 
centimeter of water to prevent lumping and then 10 cubic centimeter of concen- 
trated hydrochloric acid (specific gravity, 1.19). The material shall be ground 
with the flattened end of a glass rod until attack is complete. The solution shall 
then be evaporated to complete dryness on a steam or water bath. To hasten 
dehydration, the residue may be heated to 150° C. or even 200° C. for one-half to 
one hour. The residue shall be treated with 10 cubic centimeters of hydrochloric 
acid diluted with an equal amount of water. The dish shall be covered, and 
the solution digested for 10 minutes on a steam bath or water bath. The solu- 
tion shall be diluted to 75 cubic centimeters, filtered into a beaker, and the 
separated silica washed thoroughly with hot water. 3 Five cubic centimeters of 
concentrated hydrochloric acid and two drops, of methyl red indicator (0.2 per 
cent alcoholic solution) shall be added to the filtrate 4 (about 250 cubic 
centimeters!). 
3 Since this procedure does not involve the determination of silica, a second evaportation 
is unnecessary. 
4 Manganese, if present, is distributed between the precipitates of iron and alumina. 
calcium, and magnesium. In the amounts usually present in Portland cement it may be 
neglected. If it is desired to determine the small amount of manganese that may be 
present in the magnesium pyrophosphate, this may be done colorimeterically as describi 1 
in the U. S. Geological Survey Bulletin No. 700 (9, p. t53). If present in larger amounts. 
manganese should be precipitated with the iron and alumina, preferably by the persulphate 
method (U. S. Geological Survey Bulletin No. 700 <<>, p. 112)). If this method is used 
more aluminum passes into solution than in the method above described. 
