REPORT OF PROF. FRANCIS A. WILBER 357 



7. Observation of the effect upon the samples of high temperature with 

 sudden cooling. 



The results of these examinations appear in the table in columns 5, 14-17- 

 20, 22, 23, 24. 



Description of the methods used in the above physical examinations. 



I. Specific gravity. — This was determined by weighing the specimens- 

 previously dried, to a constant weight at a temperature of 212^ F., then im- 

 mersing them in cold water, distilled, freed from air by boiling. The vessel 

 containing the specimens was placed in the receiver of an air-pump, and a 

 partial exhaustion of the air of the receiver very soon allowed the water to 

 completely saturate the specimens. The}^ were then weighed in water and 

 the specific gravity computed in the usual manner. 



Weight of dry specimen in air 

 Specific gravity 



Weight of dry specimen in air— Weight of specimen in water 



The weighings were made upon a Becker's analytical balance, and the sam- 

 ples used weighed from twenty-five to fifty grams. The weight of a cubic 

 foot of each stone was computed from the obtained specific gravities, and 

 the results will be found in column 6 of the table. 



2. Determination of the percentage of water absorbed by the dry sample. — 

 Specimens weighing about fifty grams were used. They were dried in an 

 air-bath to a constant weight, at 212'"* F., and were then immersed in cold 

 (previously boiled) distilled water, and after complete saturation were re- 

 moved, one by one, from the water, their surfaces quickly dried with blot- 

 ting-paper, and were again weighed. The percentage gained in weight by 

 the saturated sample was then computed. 



Weight of wet sample — Weight of dry sample 



Per cent gained = X 100. 



Weight of dry sample 



See column 14. 



3. Determination of the effect of continued action of carbonic acid gas 

 upon the wet samples.— The water-saturated samples used in determining 

 the per cent of water absorption were put upon a perforated shelf under a 

 large bell-jar. The bell-jar was placed in a shallow pan, and enough water 

 poured into the pan to make a water-seal for the bell-jar. Inlet and exit- 

 tubes were introduced into it and a stream of washed carbonic acid gas passed 

 into the jar until all air was expelled. The openings were then closed and 

 the contents allowed to stand three days at a temperature of about 70*^ F. 

 Carbonic acid gas was again passed in, and this operation was repeated, at 

 intervals, during the fifty-two days of the continuance of the test. The sam- 

 ples were then removed and soaked for four days in distilled water, and 

 were afterward dried in an air bath, at a temperature of 21 2^^ F., to constant 

 weight. The per cent of loss was calculated. 



Weight of dry sample before treatment— Weight of dry sample after treatment 



Per cent loss — X 100. 



Weight of dry sample before treatment 



