296 The Philippine Journal of Science 1919 
The construction of fig. 2 is based on the results in Tables I, 
II, and III, and several hundred other analyses and physical 
tests. The figure is a diagram showing in general the relation 
of sulphuric anhyfride content, from 0 to 2.50 per cent, to 
the setting time, in both plant and laboratory samples. Be- 
cause of the considerable variation areas have been substituted 
for the usual graphs. The shaded areas represent plant sam- 
Per cent sulphuric anhydride. 
0.5 / 
180 
Pe Sina Se SIS oak SEF 
Time in minutes. 
60} 
A 
Fic, 2. Diagram showing the relation of initial set to sulphuric anhydride content. 
ples. When the sulphuric anhydride content of a cement is less 
than 1.50 per cent, it will set in only a few minutes and its 
place on the diagram is within the rectangle ACDB. Between 
1.50 and 1.80 per cent, the behavior is erratic. It may have 
a flash set or a normal set—rectangle DJIE. Above 1.80 per 
cent, the cement has a setting time of two to four hours. The 
area MHGL shows the behavior of laboratory samples. The 
average time of set is the same, with or without gypsum. 
CONTROL OF GYPSUM AT THE PLANT 
On the basis of the diagram just described, the gypsum con- 
trol at the plant was adjusted a year ago and there has been 
no further difficulty with that phase of the manufacture. With 
the present raw materials and plant equipment, the sulphuric 
anhydride content must be kept between 1.80 per cent and 2.10 
