BaILey. | Manufacture of Plasters. 169 
Some Problems Proposed for Investigation. 
In the practical working of the process of making plaster of 
Paris or cement plaster, there are numerous questions con- 
stantly arising in the mind of the thinking manufacturer, and 
the solution of many of these problems would improve the proc- 
ess of manufacture and render the product of more constant 
composition, so that the artisan could always calculate upon the 
behavior of the material under certain fixed conditions. This 
is of great importance, as in cases of unsatisfactory work there 
is always a tendency for the manufacturer to blame the man 
who uses the plaster for his wrong methods of use, and on the 
other hand for the artisan to assume that the material was not 
properly made. A. few of these problems, upon which more 
light is needed, may be mentioned here. 
What is the effect of sand or of other insoluble material upon 
the material made from the gypsite or from gypsum rock? 
What is the effect of calcium carbonate upon the same ma- 
terial? 
Is magnesium carbonate of any value in the material or is it 
detrimental? 
What material can be best used to improve the quality and 
at the same time hasten the setting of plaster used for dental 
purposes? 
Can any precautions be taken so that there shall not be a 
tendency to ‘‘streak,’’ when pure white plaster is spread o over 
a first coat of gypsite plaster? 
Which is better, a fine or a coarse sample of plaster, when 
considered with reference to its sand-carrying quality ? 
Is any of the material, strictly speaking, hydraulic, and if so, 
what tends to increase this quality ? 
Is there any relation between the specific gravity and the 
strength or setting time of the material ? 
What is the best material to use as a ‘‘ retarder, 
is its effect on the strength of the set plaster ? 
To answer these questions properly will require much time 
and many careful tests. These must be made in connection 
9) 
and what 
