CHAPTER VI. 
TECHNOLOGY OF GYPSUM. 
General Properties. 
While gypsum rock was known to the ancient investigators 
and used in those early times as fertilizer, and burned to form 
the plaster of Paris, its composition and most of its properties 
were not known or even investigated. 
LAVOISIER’S EXPERIMENTS. 
The first experiments along this line were made by Lavoisier 
and published by him in the proceedings of the Académie de 
Sciences in 1765, He decomposed the gypsum rock by means of 
carbon, and sulphurous vapors were set free with the formation 
of a sulphur deposit which showed the presence of sulphuric 
acid. He then decomposed a solution of gypsum in water by 
means of potash, and showed the presence of lime. 
After finding the elements composing gypsum, Lavoisier tried 
a synthetic experiment to prove the composition as determined, 
and he thus describes the result : 
‘*T then took concentrated sulphuric avid of which the weight was about 
double that of the water, and of known purity; I added more water, and I then 
added carbonate of lime until there was no more effervescence. I thus obtained 
a selenite which is a true gypsum.’’*” 
Thus at a very early day the qualitative composition of gyp- 
sum was determined by very careful work by one of the found- 
ers of chemical science. | 
Later quantitative analyses were made of various specimens 
of gypsum. One of the early analyses was made of the white 
37. Academie des Sciences, 1765. 
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