GRIMSLEY. | Technology of Gypsum. 117 
the air then carbonates, little by little, the excess of lime in the 
plaster, giving increased solidity and hardness to the plaster. 
Kaur and Knop hardened plaster casts by sponging the sur- 
face with one part potassium hydrate with milk whey free from 
fatty matter. Four parts of this mixture were added to a 
syrupy solution of potassium silicate, and the result was much 
harder casts. 
The hardened cement plaster is made at one mill in Kansas, 
at the Best Brothers’ mill, at Medicine Lodge (see Plate XXV ). 
The gypsum blocks are burned in the kiln and then treated with 
asecret solution and reburned. This plaster withstands a crush- 
ing force of 3000 pounds and a tensile strain of 698 pounds after 
seven days in air. It is claimed to be equal to the imported 
Keene’s cement and superior to Portland cement for plastering 
purposes or for laying dry walls. This cement is not used 
much in Kansas, but has been received with favor in the east- 
Siri) Cugies. 
Hardening of Gypsum Biocks.*? 
Experiments have been make from time to time on harden- 
ing the soft gypsum stone. Many of these have been success- 
ful, but they have not attracted much attention. Renewed 
interest has been taken in this line of work in the last few 
years. A company in Chicago have hardened gypsum for in- 
side finish for some of the public buildings in that city. At 
the present time a strong company is organized to build a mill 
in Colorado for the purpose of hardening gypsum and supply- 
ing it to the trade for inside ornamental finish to take the place 
of onyx and marble. They claim that the material is as durable 
as marble and can be suppled very much cheaper. ‘The speci- 
mens which they have already treated show that the product 
has very much the appearance of marble, and there is without 
doubt a good future for this new industry. The process used 
by the Colorado company is a secret one and little information 
can be obtained about it. 
Some processes for hardening gypsum have been patented 
_ 42, Mr. C.C. Quincey, of Chicago, has furnished the writer with the copies of patent specifica- 
tions in this section and of retarders already given. 
