281 
November 6th, 1871. 
The President in the chair. Nineteen persons present. 
Pror. T. EGLESTON remarked that one of the most inter- 
esting, perhaps the most interesting machine in the late Fair 
of the American Institute, was the Sand Blast Machine. He hap- 
pened accidentally to be present when the judges made their 
examination of it, and saw all the usual experiments shown, 
such as etching of fine lace on glass without injuring the lace, 
cutting letters and ornaments on limestone and drilling a hole 
through a file, and while admiring the beauty of work and: 
thinking of the numerous commercial applications of which 
it was capable, a series of experiments suggested themselves, 
which through the liberality of the managers of the Fair, he 
was able in part to carry out. By an unfortunate misunder- 
standing the verbal request that he would commence the 
experiments did not reach him, until two days before the close 
of the Fair, though sent a week previously. The experiments 
were to have been, the examination of the effect of the sand 
blast, on rocks and mineral aggregates, the substitution of 
pulverized minerals of different hardness for the sand in the 
machine, and the examination of the effect of these sands on 
harder bodies. It was possible only to carry out the last 
part of the plan, and that too only partially. The sand blast 
proved to be so much more powerful than could have been 
imagined, that it was necessary to entirely rearrange the ex- 
periments after they had been commenced. 
The minerals chosen were Corundum in crystals from 
Delaware Co., Pa. a piece of Emery, from Chester, Mass., 
composed of a mixture of Corundum and Magnetite. <A 
pebble of Topaz of the variety known as Goute d’Hau. A 
large Topaz pebble colorless and transparent, with a large 
cleavage face, and a black Diamond. The following table 
gives the results of these experiments. 
