STATE GEOLOGIST. 135 
gravimetrically. One-half gram of pure spar should exactly neutralize 
EF OuGcuOneacia: 
Weigh out ™% gram of a finely ground limestone, transfer to an 
Erlenmeyer flask of about 500 cc. capacity provided with a rubber stop- 
per and a thin glass tube 30 inches long, to serve as a condenser. Run 
into the flask 60 cc. of the 1-5 normal acid, attach the condenser and boil 
gently, allowing no steam to escape from tube, for about two minutes. 
Wash down the tube into the flask with a little water. kemove the con- 
denser and cool the solution thoroughly by immersing the flask in cold 
water. When quite cold add five to six drops of phenol-phthalein solution 
(I gram in 200 cc. alcohol) and titrate back to first pink color with 1-5 
normal caustic soda solution. It is important to recognize the point at 
which the first pink color appears throughout the solution, even though 
this may fade in a few seconds. If the alkali be added to a permanent 
and strong red color the lime will come too low. The amount of acid 
used is called the first acid and the alkali used to titrate back, the first 
alkali. : 
In case the materials contain a very small amount of magnesia the 
operation ends here and the calculation is simply: Number of cc. acid 
minus number of cc. alkali multiplied by 20.56=per cent. calcium oxide. 
In this case it is unnecessary to cool the solution, and a permanent red 
is obtained at the point of neutralization. 
The determination of magnesia proceeds as follows: 
Transfer the neutral solution to a large test tube 12 inches long 
and 1 inch inside diameter marked at 100 cc. Heat to boiling and add 
I-5 normal caustic soda solution, about one cc. at a time, boiling for a 
moment after each addition until a deep red color is obtained which 
does not pale on boiling. 
This point can be easily recognized within one-half cc. after a little 
practice. Note the number of cc. soda solution added to the neutral solu- 
tion as second alkali. Dilute to 100 cc., boil for a moment and set the tube 
aside to allow the precipitate to settle. When settled take out 50 cc. of 
the clear liquid by means of a pipette and titrate back to colorless with 1-5 
normal acid. Multiply by 2 the number of cc. of acid required to 
neutralize and note as second acid. 
Calculation : 7 
Second alkali: second acidx20.40=per cent magnesia. First 
acid (1st alkalit-2nd alkali—second acid) X20.56=per cent. calcium 
oxide. 
Method 3.—The volumetric determination of carbon dioxide from 
calcium carbonate, though used to some considerable extent in Europe, 
has not found favor among American cement chemists, who prefer other 
volumetric methods. The Cramer-Baur burette is one of the most con- 
venient apparatus for this purpose. 
