Chemical and Physical Papers. 71 



pebble mill. This dust, sifted through No. 7 bolting cloth, is 

 mixed with water into a stiff dough, allowed to stand for twenty- 

 four hours in tight jars, and then pressed by hydraulic power, with 

 a maximum of 100 kilograms per square centimeter ( 1400 pounds 

 per square inch), into cylinders one inch high and one inch in di- 

 ameter (2.5 centimeters). These are oven-dried for twenty-four 

 hours and then broken by blows in the Page machine. The blows 

 are given by a one kilogram (2.2 pounds) rain falling a distance 

 of one centimeter, the number of blows needed to fracture the 

 briquet being taken to represent the cementing power of the ma- 

 terial. Five briquets were tested for each sample. This test is 

 of great value, but the methods of making it have not as yet been 

 worked out with entire satisfaction. An impact test of a rain, fall- 

 ing in a small machine like a pile-driver on a small block cut from 

 the actual stone, is often made, but this is not included in this 

 series. 



In the freezing and thawing tests, ten pieces of the stone to be 

 tested were first dried thoroughly, then saturated, and frozen by be- 

 ing placed in the open air. When the temperature fell to 20 de- 

 grees F. or lower, the stone was considered sufficiently frozen. 

 The stone was then thawed by steam, resaturated.'and again frozen. 

 After as many alternate freezings and thawings as would be ob- 

 tained last winter, the loss of weight was determined. Also the 

 stone that had been subjected to this process was put through the 

 Deval machine and its loss by abrasion compared with that of un- 

 frozen samples. The results have not been very satisfactory, because 

 of the limited cold weather of last winter, the insufficient number 

 of tests, and the experimental stage of the matter. On all samples 

 tested there was a slight loss, due to freezing and thawing, varying 

 from 0.28 per cent, to 1.25 per cent. The Deval test on stone sub- 

 jected to the freezing test showed a loss sometimes larger and some- 

 times smaller than that from untreated stone. It is likely that the 

 test may prove of some value, but there has been too little work 

 done to warrant any conclusions. 



Determinations of weight, specific gravity, porosity and^absorp- 

 tion were also made. 



Following is a table showing the results of the tests of the years 

 1905-'06 : 



