116 University Geological Survey of Kansas. 
gypsum. He tried mixtures of plaster with sulphates of soda, 
of potash, of ammonia; but on account of the amount of water 
in these salts, the results were not satisfactory at first. By 
changing the proportions of the salts so as to saturate the car- 
bonate of lime in solution, the results were good, and a hard 
plaster was formed. 
Landrin placed the crude gypsum in a ten per cent. solution 
of sulphuric acid for fifteen minutes, and then calcined it, and 
obtained a plaster of good set and hardness. Heat must be ap- 
plied in sufficient amount to drive out all the sulphuric acid, 
and the best temperature was found to be between 600° and 
700° F. Hydrochloric acid was used, but with poor results. 
By the Greenwood hardening process, gypsum is burned in 
the usual way and then placed in an eight or ten per ceni. solu- 
tion of alum. After soaking for some minutes, the gypsum is 
drained and dried in the air and burned again at a dull red 
heat, but not above this temperature. 
Keene’s patent cement is made by drying a mixture of plas- 
ter of Paris with one part borax, one part cream of tartar, and 
eighteen parts of water. The mixture is burned at a low red 
heat for six hours. 
Parian cement is made from gypsum hardened by means of 
borax. One part of borax is dissolved in nine parts of water, 
and the gypsum is treated with the solution. Sometimes one 
part of cream of tartar is added to the solution, with good 
results. 
Attempts have been made to harden the gypsum with water 
glass solution, but it is not always satisfactory. | 
Landrin, in his experiments, found that lime had great in- 
fluence on the plasters. By mixing lime with the plaster in 
different proportions he obtained plaster which set regularly 
and became very hard and took a high polish. He states that 
it is better not to use over ten per cent. of lime. lLandrin’s ex- 
planation for this change is that the hme in contact with water 
sets free heat, which evaporates the quantity of water not nec- 
essary to bring the hydrate plaster back to its original gypsum 
state, with its two molecules of water. The carbonic acid of 
