20 BULLETIN 949, U. S. DEPARTMENT OF AGRICULTURE. 
INSOLUBLE RESIDUE. 
(22) To a 1-gram sample of cement shall be added 10 c. c. of water and 5 c. c. of 
concentrated hydrochloric acid : the liquid shall be warmed until effervescence ceases. 
The solution shall be diluted to 50 c. c. and digested on a steam bath or hot plate 
until it is evident that decomposition of the cement is complete. 
The residue shall be filtered, washed with cold water, and the filter paper and 
contents digested in about 30 c. c. 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 hydro- 
chloric 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 results 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 c. c. of concentrated hydro- 
chloric acid diluted with 5 c. c. of water, with gentle warming: when solution is 
complete, 40 c. c. of water shall be added, the solution filtered, and the residue washed 
thoroughly with water. The solution shall be diluted to 250 c. c. heated to boiling, 
and 10 c. c. 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 be digested on the steam bath until the precipitate has 
settled. 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 
naming. The barium sulphate shall then be ignited and weighed. The weight ob- 
tained multiplied by 34.3 gives the percentage 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. 
(25) 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 per cent. 
MAGNESIA. 
(26) To 0.5 gram of the cement in an evaporating dish shall be added 10 c. c. of 
water to prevent lumping and then 10 c. c. of concentrated hydrochloric acid. The 
liquid shall be gently heated and agitated 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° or even 200° C. for one-half to one hour. 
The residue shall be treated with 10 c. c. of concentrated hydrochloric acid diluted 
with an equal amount of water. The dish shall be covered with the solution digested 
for 10 minutes on a steam bath or water bath. The diluted solution shall be filtered 
and the separated silica washed thoroughly with water. Five cubic centimeters of 
concentrated hydrochloric acid and sufficient bromine water to precipitate any 
manganese which may be present shall be added to the filtrate (about 250 c. c). This 
shall be made alkaline with ammonium hydroxide, boiled until there is but a faint 
odor of ammonia, and the precipitated iron and aluminum hydroxides, after settling, 
shall be washed with hot water, once by decantation and slightly on the filter. Set- 
ting aside the filtrate, the precipitate shall be transferred by a jet of hot water to the 
precipitation vessel and 'dissolved in 10 c. c. of hot hydrochloric acid. The paper 
shall be extracted with acid, the solution and washings being added to the main 
solution. The aluminum and iron shall then be reprecipitated at boiling heat by 
ammonium hydroxide and bromine water in a volume of about 100 c. c. and the 
second precipitate shall be collected and washed on the filter used in the first instance 
if (his is still intact. To the combined filtrates from the hydroxides of iron and alumi- 
