GRIMSLEY. | Technology of Gypsum. 119 
ammonia in such places and fixes it, making a very valuable 
fertilizer. On account of its cheapness and convenience it is a 
wonder that more of the land plaster is not sold. Our farmers 
should certainly give it a trial, and they will be pleased with 
the results. 
Another use of the ground, uncalcined gypsum, which is not 
to be so highly recommended, is its use as an adulterant. Gyp- 
sum has been found to have a large use in this respect, as has 
been discovered in the various states where pure-food laws have 
been enforced, and where their chemists have made careful anal- 
yses of the various foods and medicines. It is found in flour, 
sugar, baking-powder, and other compounds. A very consid- 
erable amount is sometimes taken to cure chills and fever in its 
mixture with quinine. The land plaster has been used as an 
adulterant for white lead, where it is claimed to be beneficial. 
For these various purposes the plaster is sold under the name 
terra alba. 
When gypsum is calcined it is known as plaster of Paris. 
The finer grades are sold as dental plaster and as plaster of 
Paris for casts and moulds. It is also used for white finish on 
walls of buildings. Calcined gypsum has been used for these 
purposes from a very early day. 
The manufacture of the slow setting or cement plasters has 
been regarded as a comparatively new departure in the indus- 
try; but when Doctor Wallace* made analyses of the cements 
used in the great pyramid of Cheops, supposed to have been 
erected about 5000 years ago, these were found to be very closely 
related to our cement plasters, as shown in the analyses below : 
: K 
ELEMENTS. Inside of pyramid, | Outside of | Cement eauisiit 
pyramid. | pilaster. plaster.4° 
Sulphate of lime (gypsum)....... 81.50 per cent. 82.89 78.41 83.55 
Carbonareron limes eae es. 9.47 ue 9.80 10.79 Doe 
Carbonate of magnesia.......... 0.59 ue 0.79 1.05 1.47 
SUUNICE Bis nie Gee eect ohare ee Reena ao aauna 0.30 gs 4.30 7.82 4.27 
fa HONTAND) Se ew tee Menai ieee Aaa 44 ois 3.00 ; 
ro mwOoxt des yeas a cea nUN At prencde e a 0.25 fs 0.21 LAG Deed 
WAY ENGSIP eo) d's lo Cores sweets Meas hl eas eet TREN te ee a Hee 6.67 
MO Gals Parwveepegs Mn aula aah. 99.52 per cent. | 100.99 | 100.00 99/50 
44, Thorpe, Dictionary of Applied Chemistry, Vol. 1, on Cements. = 
45. Roman cement plaster, Springvale, Kan. Analysis by E. H.S. Bailey. 
