STATE GEOLOGIST. 111 
shoveled. onto a heavy screen consisting of iron rods, forming about 
Chan es iv MInSHsCheen, ADOUM: ay tcetmibya ei teet am Size, was 
placed within a box 15 inches deep and 3 feet square on the inside, 
and it was let down into the box about 5 inches, so there was a space 
cf about 10 inches depth beneath the screen. A smaller flat box was 
placed within the large box, under the screen, before the mill charge was 
shovelled onto the grating. The latter was just close enough to keep 
back the flint pebbles, while the ground material dropped into the box 
below. This was found to work very well, and it was a simple matter 
to prepare batches of limestone samples, or clay, or experimental cement 
mixtures. Clinker also was ground on this mill. In grinding clays or 
shales these must be thoroughly dry or the material will stick to the 
pebbles. In some cases it may even be necessary to apply a gas flame to 
the outside shell of the mill while it is running, to prevent the “pasteing”’ 
of the charge. The mill makes about 27 revolutions per minute and the 
power required to run it is quite trifling. 
The samples thus obtained are thoroughly homogeneous and any 
portion of the ground mixture is a true average. 
Though every laboratory is not in possession of such an outfit, sim- 
ilar mills, though small, may be constructed or bought with comparatively 
little expense. A small porcelain lined ball-mill driven by an electric or 
water motor will be found a valuable accessory of every technical lab- 
oratory. 
CHEMICAL EXAMINATION OF CEMENT MATERIALS. 
The chemical examination of the various substances entering into 
the domain of cement manufacture will be considered under the following 
topics : 
Natural pozzuolane materials. 
Slags, total analysis and sulphur determinations. 
Natural cements. 
Clay analysis. 
Mineral analysis of clay, by the sulphuric acid method. 
Mineral analysis of clay by heating with calcium carbonate. 
Standard methods of limestone and cement analysis. 
Commercial methods of cement material analysis. } 
9g. Determination of insoluble residue in raw mixtures and Portland 
cements. 
10. Physical supplementary methods. 
Ir. Carbon determination and coal analysis. 
12. Mechanical analysis of raw mixtures, clays and cements. 
13. Special problems in cement chemistry. 
Oo) RE ONES ORS eal 
CHEMICAL EXAMINATION OF POZZUOLALKE MATERIALS. 
Technical examination of natural pozzuolane, trass and_ similar 
hydrous materials. 
