30 BULLKTIX 121*;, U. 5. DEPARTM KXT <)V aGB I CULTURE. 
pipette and the boiling continued until the precipitate is well 
formed The solution shall he digested od the steam hath until 
the precipitate has settled. The precipitate shall he 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 he ignited and weighed. 
The weight obtained multiplied by 34.8 gives the percent- 
age of sulphuric anhydride. The acid filtrate obtained in the 
determination of the insoluble residue may ho used lor the esti- 
mation of sulphuric- anhydride instead of using a separate 
sample. 
25. A permissible variation of (>. in will be allowed, and all re- 
sults in excess of the specified limit hui within this permissible 
variation shall he reported as 2.00 per cent. 
Magnesia. 
Magnesia. 26. To 0.5 gram of the cement in an evaporating dish shall 
he added K) cubic centimeters of water to prevent lumping and 
then 10 cubic centimeters of concentrated hydrochloric acid. The 
liquid shall he gently heated and agitated until attack is com- 
plete. The solution shall then be evaporated to complete dryness 
on a steam or water hath. To hasten dehydration the residue 
may be heated to lot) or even 200° C. for one-half to one hour. 
The residue shall be treated with 10 cubic centimeters of con- 
centrated hydrochloric acid diluted with an equal amount of 
water. The dish shall be covered and The solution digested for ten 
minutes on a steam bath or water hath. The diluted solution 
shall be filtered and the separated silica washed thoroughly with 
water. 9 
Five cubic centimeters of concentrated hydrochloric acid and 
sufficient bromine water to precipitate any manganese which may 
be present shall he added to the filtrate (about 250 cubic centi- 
meters). This shall be made alkaline with ammonium hydroxide, 
boiled until there is but a faint odor of ammonia, and the pre- 
cipitated iron and aluminum hydroxides, after settling, shall be 
washed with hot water, once by decantation and slightly on the 
filter. Setting aside the filtrate, the precipitate shall be trans- 
ferred by a jet of hot water to the precipitating vessel and dis- 
solved in 10 cubic centimeters 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 cubic centimeters, 
and the second precipitate shall be collected and washed on the 
filter used in the first instance if this is still intact. To the 
combined filtrates from the hydroxides of iron and aluminum, 
reduced in volume if need be, 1 cubic centimeter of ammonium 
hydroxide shall he added, the solution brought to boiling, 25 
cubic centimeters of a saturated solution of boiling ammonium 
oxalate added and the boiling continued until the precipitated 
calcium oxalate has assumed a well-defined granular form. The 
precipitate after one hour shall be filtered and washed, then 
with the filter shall he placed wet in a platinum crucible, and 
the paper burned off over a small flame of a Bunsen burner; 
after ignition it shall be redissolved in hydrochloric acid and 
the solution diluted to loo cubic centimeters. Ammonia shall be 
added in slight excess, and the liquid boiled The lime shall 
then be reprecipitated by ammonium oxalate, allowed to stand 
until settled, filtered and washed. The combined filtrates from 
the calcium precipitates shall be acidified with hydrochloric acid, 
concentrated on the steam bath to about 150 cubic centimeters. 
and made slightly alkaline with ammonium hydroxide, boiled 
B Since this procedure dons not involve the determination of silica, a 
second evaporation is unnecessary. 
