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CHEMISTRY AND PHYSICS. 
MANUFACTURE OF CEMENT PLASTER. 
In the process of manufacture, the ordinary iron kettles are used, of a capac- 
ity of about eight tons of crude material. These kettles are heated by a coal 
fire directly on the bottom and the flame is carried around the sides in flues. 
Each kettle is provided with a mechanical stirrer making fifteen revolutions per 
minute. Anexcellent quality of coal is used so as to produce as hot a fire as 
possible. The crude material is dropped into the heated kettle gradually till 
there is a sufficient quantity, and as the heat is applied all the time a violent 
boiling, as it is called, takes place, from the evolution of the steam of the mois- 
ture in the original material and the combined water. A short time before the 
process is complete (which requires about three hours) there is a sudden settling 
of the material and the evolution of steam ceases, but this begins to boil again. 
and after a certain time, which can be determined by the expert laborer, the 
kettle is opened at the bottom and all the material is dropped in a few seconds 
into a storage pit. The burned cement is then sifted, and any particles too large 
to pass through the sieve are ground and burned again. In the process consid- 
erable dust is carried off from the kettle and in the best mills this is collected 
and saved. 
In order to study the process of manufacture more completely, I have made 
analyses of the material in the process as follows: 
No. 1, crude gypsite. 
No. 2, the completed ‘‘ cement plaster.”’ 
No. 3, dust thrown off from the material while being calcined. 
No. 4, tailings from the bolting reel. 
No. 5, sample of the ‘‘ set ‘’ cement plaster. 
Nos. 2, 3, 4 and 5 were from the same kettleful of cement, while No. 1 isa 
mixture of twelve samples of the crude material as it was running into the kettle. 
In order to arrive more fully at the composition in this case the carbonic acid 
was determined by actual weight, after decomposing with hydrochloric acid, and it 
will be noticed that there is not a sufficient quantity to combine with the cal- 
cium and magnesium. This seems to indicate that some of the bases are in the 
combination with silica in the form of clay or other soluble minerals. 
Silica and insoluble residue....} 12.29 14.31 13.48 22.02 12.03 
Tron and aluminum oxids..... Peat 2.16 Ph Bs" OO 1.62 
Calenmrsulfatens).-2-.cex ce: 57.95 66.22 66 .52 53.67 59.37 
@aleinim carbonate.......- o.+. 8.01 9.42 6253 LOT 8.07 
CalerummioOxiG sth, ee teh auet eae, 1.85 2.56 4.70 1.89 
MaenesiumiOxiGs<...4.2<5..5-2 .18 91 .59 .56 61 
\WVEASTE 5 oe a oe iret A ee ae Sad 16.07 4.91 6.78 4.43 16.38 
BRO tals .e aa er eee Se le Anes 99.49 99.78 98.79 99.78 99.97 
It is interesting, also, to notice in this connection that the set cement agrees 
remarkably in composition with the original crude sample. It has just about 
the same quantity of water that was originally present. 
In the dust there is present 6.78 per cent. water, which shows that some of 
the material not fully calcined had been carried off from the kettles. The tail- 
ings contain more of the silica and insoluble material. This is to be expected, 
as those are the parts that have not so readily broken up under the influence of 
heat. As the heat is carefully kept below a 400° F., there seems to be little pos- 
