474 PROCEEDINGS OF THE AMERICAN ACADEMY. 



tion used here is the same as that used hy Tammann. In the present 

 work this variety of ice was found in another way, coming fi'om high to 

 low pressures at about —22°, and from the domain of stability of a vari- 

 ety of ice stable only at higher pressures. It was obtained first with 

 the same apparatus as that used on the I-L curve. Two points on 

 equilibrium curve I-III and two unsatisfactory measurements of the 

 change of volume were made with this apparatus, but all the subse- 

 quent determinations were made with the apparatus especially de- 

 signed for low temperatures. A short description of this new apparatus 

 will not be out of place. 



This had three different pressure chambers instead of only two as 

 formerly. The upper cylinder in which pressure was produced by the 

 advance of the piston was the same as that used before. This was 

 jacketed with running water from a large tank, so as to be maintained 

 at a constant temperature. Communicating directly with this, and ex- 

 posed freely to the air of the room, was a block of nickel steel with 

 provisions for three connections. In one of these holes for connections 

 was placed the manganin resistance plug with which pressure was 

 measured. No temperature correction had to be applied to the readings 

 of this, therefore. The third connection in the block was to the cylin- 

 der containing the water to be experimented on. This cylinder was 

 of hardened nickel steel, 8 inches long, 1 inch o. d., and 1/2 inch 

 i. d. The water to be experimented on was placed directly in the cylin- 

 der, nearly filling it. The remainder of the cylinder was filled with 

 gasolene communicating through the connecting block with the pres- 

 sure-producing cylinder. Some hesitation was felt at first about al- 

 lowing the water to completely fill the interior of the cylinder, instead 

 of being placed in a cyhnder exposed to pressure on all sides. Fear 

 was felt that the water in freezing might so expand itself against the 

 sides of the cylinder as to be able to support an appreciable stress, so 

 that a hydrostatic pressure applied by means of the gasolene to the up- 

 per part of the frozen ice cylinder would not be transmitted uniformly 

 to all parts of the mass of ice. In the first few experiments an at- 

 tempt was made to avoid the possibility of the effect by providing 

 means for the gasolene to penetrate to the neighborhood of all parts 

 of the ice. This was done with a tube of very thin sheet copper, closed 

 at the bottom, but open at the top to the gasolene, placed axially in 

 the cylinder, and extending throughout the mass of water. The pre- 

 caution proved needless, however, since there were no discrepancies to 

 be ascribed to this cause when the device was omitted. 



It was necessary to use gasolene as the transmitting fluid because of 

 the low temperatures. Kerosene becomes too stiff to transmit pres- 



