STATE GEOLOGIST. WAL 7 
Tn the united filtrate from the calcium the magnesium is determined. 
Add to the cold liquid, 25 cc. of saturated solution of sodium diphosphate 
and excess of ammonia. The amount of solution should not 
exceed 400 cc. Stir thoroughly and let stand for 12 hours, especially 
when much magnesia oxide is present. Filter and wash with water con- 
taining about 10 per cent. of its volume of ammonia and some ammonium 
nitrate, about 100 grams to the liter. Dry and ignite the precipitate, which 
is magnesium pyrophosphate. 
In examining natural cements it is sometimes necessary to determine 
the carbonates still present after burning, so as to obtain a numerical 
expression for the completeness of the burning. This 1s done by expelling 
the carbon dioxide with hydrochloric acid and absorbing the gas as usual 
in potash bulbs. 
It may be desirable to make the determination of unburnt carbon 
in a natural cement. ‘This is carried out with a sample treated with 
hydrochloric acid in order to decompose any carbonates present. After 
the acid treatment and expulsion of the free acid the sample is burnt in 
regular combustion tube, or a Shimer crucible, the carbon dioxide being 
absorbed in potash bulbs. 
For rough approximation of the amount of water of hydration, car- 
bon dioxide and carbon present in natural cements simple heating over 
the blast lamp will usually suffice. 
COMPLETE ANALYSIS OF CLAY. 
Fuse 1% grams of the clay with 10 grams of sodium carbonate 
and separate the silica by double evaporation as given under the examina- 
tion of natural cement. Test the weighed precipitate with hydrofluoric 
acid and any residue remaining, usually very small, should 
be considered as alumina. It is absolutely necessary to carry out the 
Couble evaporation, as without it no satisfactory results can be obtained. 
Iilter the silica through a 11 cm. ashless filter. The evaporation should 
be done on a hot plate or asbestos stove. Irequent stirring during the 
pasty stage of evaporation is necessary. 
The amount of silica obtained multiplied by 0.666 will give the silica 
in one gram. | 
Now transfer the filtrate from the silica determination to a 
flask calibrated to hold 600 cc. Retain of this volume 4oo cc. for 
the determination of alumina and ferric oxide, lime and magnesia, and 
remove 200 cc. for the determination of iron by the bichromate 
method. The amount of iron found is of course multiplied by 2 to 
obtain the ferric oxide in one gram of sample. This procedure is much 
more rapid than the determination of iron by the permanganate method. 
If the latter is used, precipitate with ammonium hydroxide, the alumina 
and iron in the portion of 200 cc. which has been removed, decant the su- 
pernatant liquid and transfer the precipitate to the filter and wash it 
