59 
fully of the waters of the Delaware River collected just 
above tide water at Trenton, in 1856, (See Am. Jour. of 
Science, xxii, 154,) gave the proportions when all the lime 
was calculated as carbonate, of 100 of the latter to 31-7 of 
silica. Doubtless the great difference in the geological 
surfaces of drainage systems of the St. Lawrence and 
Delaware will serve to explain the variation from Hunt’s 
results. 
The following paper was read, 
On Volatile Liquids suitable for Ice Machines. 
By Pror. CHarues A. SEELY. 
The Twining ice machine comprises three essential parts, 
which may be called the freezer, the vapor pump and the 
condenser. ‘These are arranged in the order named, and the 
condenser is joined with the freezer, so as to form the series 
into a closed circuit. When the machine is in action, the 
volatile substance continually flows or circulates in the 
circuit, taking away heat from the water of the freezer, and 
giving it up at the condenser; the volatile substance is the 
conveyor or vehicle for heat, loading at the freezer, and dis- 
charging its burthen at the condenser. 
The power consumed in working the ice machine, may be 
divided into two parts, that which is directly and only con- 
cerned in the freezing, and that which is used in meeting 
what are termed practical difficulties. The calculation of the 
first is the simplest of problems, for its terms and conditions 
are few, well known and invariable. A unit of heat or of 
cold if one chooses, measured by gravity, is 772 foot pounds, 
that is, to heat or to cool one pound of water, one degree re- 
quires a force equivalent to 772 ft. Ibs) The freezing of a 
pound of water at 82° to ice at 32° represents (143.772) 
110,396 ft. lbs) One pound of pure Carbon develops 8,000 
heat units in its combustion, and this amount of energy ex- 
pended directly in freezing water, will produce 56 lbs. of ice; 
