144 University Geological Survey of Kansas. 
Methods of Analysis. 
Without giving the details of the analysis, with which all 
chemists are familiar, a few points should be noted. In dis- 
solving the mineral, of which at least two grams is used, in 
hydrochloric acid and evaporating to dryness to render silica 
insoluble, when again’ dissolving in hydrochloric acid, there is 
danger that an error may be introduced by not treating the resi- 
due persistently enough with hot dilute hydrochloric acid. This 
is on account of the insolubility of calcium sulphate in concen- 
trated acid, unless used in large quantities. It has been our 
practice to boil the so-called insoluble residue repeatedly with 
about a ten per cent. solution of acid, and to repeat this till the 
bulk of the residue does not diminish. 
After the separation of silica, the filtrate is diluted to 500 ¢. c., 
and of this, 200 c. c. are used for the determination of the bases 
and 200 for sulphuric acid. This obviates making asecond weigh- 
ing of material for the acid. The precipitate of barium sulphate 
must be purified after weighing, by treating with dilute hydro- 
chloric acid, filtering, and again weighing. It has been found 
advisable to precipitate the calcium oxalate twice, and to evap- 
orate the filtrate in a beaker to dryness, on an iron plate, with 
an excess of nitric acid. By this means only a very small resi- 
due remains, as the ammonia salts have been changed to nitrate 
and decomposed into nitrous oxide and water, or have been 
driven off as sulphate or chloride. This leaves the magnesia 
salts with very little to interfere with their complete precipi- 
tation. 
Water can be determined either by heating in an air bath at 
200° C. to constant weight, or directly over a lamp turned so 
low that there shall be no danger of driving off carbon dioxide. 
In cases where carbon dioxide has been determined, it has 
been done with greatest success by direct absorption in a potash 
bulb or in soda-lime, by the apparatus that is familiar to chem- 
ists. The apparatus in which the carbon dioxide is driven off 
and the amount calculated by loss in weight gives good results 
in the hands of one who has become sufficiently expert in its 
manipulation. 
