558 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



to it, but these are generally given by those least competent to 

 judge. The College of Physicians made a series of observations 

 for the guidance of their judgment. Dr. Rogers tested the tem- 

 perature of the salt slush in many places, and he walked through 

 the streets with a thermometer in his hand, carrying it about 

 three feet above the ground. He found the slush but very few 

 degrees colder than the snow — three, four, five, and, in one. case, 

 eight degrees colder; and the temperature of the lowest stratum 

 of the air was, in no case, any lower than that at the height of 

 five or six feet. Both boards gave their opinion in favor of 

 allowing salt to be used, and no physician objected to it. 



Since the last meeting I have very fortunately had an oppor- 

 tunity of making some experiments myself. We had a slight fall 

 of snow, and 1 prepared some mixtures of it with ss^lt, in differ- 

 ent proportions, and observed the temperatures and the rate of 

 melting. I placed in my laboratory four tin cans, all of the same 

 size — six inches in diameter and eight inches in height. In each 

 of these I placed twenty ounces of snow, carefully weighed. In 

 one of the cans, which I call number one, I mixed with the snow 

 ten ounces of salt, in number two I mixed one ounce, in number 

 three one-fifth of an ounce, and in number four I left the snow 

 pure, without any mixture of salt. It will be seen that in num- 

 ber one the proportion (5T salt was fifty per cent, of the weight 

 of snow ; in number two, five per cent. ; and, in number three, 

 one per cent., the last being about the proportion in which it is 

 used in the streets. I tried the temperatures of the mixtures with 

 a thermometer at several periods during the day, with the follow- 

 ing results : 



A. M. P. M. 



9:15 9:45 10:45 11:45 12:45 1:45 4:00 Salt. Snow. 



Temp, of air. 47° 50° 62° 55° 58° 6G° 60° — ^^> .^^.^ 



Can No. 1, temp. —4° —3° —1° 18° *30° 39° 48° 10 oz. 20 oz. 



Can No. 2. temp. 0° S** 7° 18° 21° 27° 43° 1 oz. 20 oz. 



Can No. 3, temp. 4° 19° 22° 28° 28° 30° *31° i oz. 20 oz. 



€an No. 4, temp. 32° 32° 32° 32° 32° 32° 132° oz. 20 oz. 



The four deg. belew zero, entered in the memorandum as hav- 

 ing been observed at fifteen minutes past nine, A. M., is a mean 

 from observations in different parts of the vessel. In some parts 

 it was six deg., which was the lowest temperature noted. The 

 snow M'^as unfortunately damp, and it was impossible to mix the 

 salt with it as thoroughly as would have been desirable. It will 

 be seen from the table that No. 1 was all melted at 12:45 P. 



* No snow. t Much snow still unmelted. 



