72 



CEMENTS, LIMES, AND PLASTERS. 



"The observed diminution of volume corresponds to expectation, 

 regard being had to the molecular volumes at 25: 



Hence for 



CaS0 4 + 2H 2 = CaS0 4 2H 2 0, 



"The observed diminution of volume satisfied this requirement even 

 quantitatively, inasmuch as 11.63 grams of floor-gypsum caused an 

 expansion of 0.63 c.c., that is to say, 0.054 per gram, while calculation 

 gives 0.057. It may be added that the water content of the mass formed 

 (20.6 per cent) corresponded to the total transformation into gypsum 

 (20.9 per cent). 



" With the aid of this method we traced the influence which the 

 burning temperature has on the setting capacity. In particular we 

 investigated the contradictory statements whether the formation of 

 the gypsum capable of setting takes place at a temperature higher 

 than that at which dead-burning ensues or whether with rising tem- 

 perature the binding capacity is gradually lost. This determination is 

 important, for according to the above statement a dead-burned gypsum, 

 and probably also the natural anhydrite, would acquire binding capacity 

 by appropriate burning. Let it be stated at once that, so far as our 

 observations go, the binding capacity decreases regularly with increas- 

 ing burning temperature. 



" In this respect we had previously found that an anhydrite pre- 

 pared at 100 hardens even more quickly than stucco gypsum. A real 

 burning can only be spoken of above 190, for it is only above that 

 temperature that the water develops out of half-hydrate at a tech- 

 nically utilizable rate. Hence we first of all heated samples of well- 

 crystallized half-hydrate (obtained from gypsum with nitric acid) 

 200 and 300 for ten hours each. The volume experiment show< 

 in the case of the latter sample a decrease of binding capacity: 



200 ; 2 . 624 gr. Capillaries : 1 mm. = . 00382 c. c. 



300; 2 gr. Capillaries: 1 mm. =0.00323 c.c. 



