The cost of harvesting a ton of natural ice varies greatly, it depending to a great extent upon the weather conditions, both during the process of the formation of the ice and during the process of cutting and housing. Under average conditions the cost of harvesting amounts to about 80 cents, though under favor able conditions it has cost only from 25 to 30 cents per ton, but this is exceptional. This, of course, does not include the cost of transporta tion, delivery, etc., and as the majority of the icehouses are a considerable distance from the centres of consumption, the cost of transporta tion is a large factor.
The moving of this enormous quantity of ice necessitates the maintenance of a large fleet of barges and other boats for the domestic trade, and of sailing vessels for the export trade. and to the cost of maintaining these vessels, when figuring the cost of harvesting, must be added the cost of towing, loading, discharging, dock and stable rent, repairs of boats, icehouses and wagons, etc., all this before the ice is placed in the hands of the retailer.
Since 1900 the natural crop has tended to reduction owing to increased use of artificial ice. Not much natural ice is now used south of Baltimore and Washington, and these cities use very large quantities of artificial ice.
The tools used in harvesting this crop are many and varied. Many of them were invented by Nathaniel Wyeth and John Barker of Bos ton. The ice plow was invented in 1839 and the patent clearing-tooth in 1872. Some of the most common tools now in use are: the snow scraper or plane, the masher and the plow; augers and axes for tapping the ice in order to drain off surface waters; saws; forked bars for prying the cakes loose; various forms of hooks for handling the cakes; trimming bars for squaring the cakes after loose; adzes, edg ing tongs and chisels used in packing the ice when in the storehouse; saws and bars for pry ing loose previous to shipment; and tongs, scales, axes, etc., used on the retatl delivery wagon.
Artificial Ice.— The manufacture of ice as an industry was begun as early as 1866, but only reached a degree of commercial importance about 1880. The beginning was naturally made in the Southern States, but as it became more generally used, factories sprang up over the entire country. The growth of the °infant in dustries') throughout the United States gave this industry an added stimulus, because the supply of natural ice was by far too small to meet the requirements of slaughtering and meat packing-houses, refrigerator cars, cold-storage warehouses, etc.
The first experiments for making artificial ice for mercantile uses started with the Italians in the 16th century. The first machine used for the actual manufacture was invented by Dr. William Cullen, this being based on the vacuum principle, the atmospheric pressure being re duced by means of an air pump. Later, in 1795, several experiments were made by a Mr. Walker of Oxford, England, in the line of freezing mixtures. Professor Leslie of England pro duced a considerable degree of refrigeration by including in the exhausted receiver of an air pump sulphuric acid, a substance rapidly ab sorbing vapor. In 1834 Jacob Perkins, an American engineer residing in London, ob tained a patent for a machine generally credited with being the forerunner of the modern com pressor machine. The refrigerant used in this machine was ether and brine, and was circu lated at a temperature of 5° Fahrenheit through pipes which encircled the evaporator containing the ether. After running through the pipes, the brine flowed into a receptacle containing boxes filled with water and thus the water was frozen. Later experiments were made by French and German inventors, boxes being sup planted by cans, and this developed into the manufacture of can ice. Many of the improve ments made in the ice-making apparatus are due to the efforts of Prof. A. C. Twining of New Haven, Conn. He patented an ice machine in England in 1850 and in the United States in 1853; in 1855 he invented a machine and put it into active operation in Cleveland. Ohio, which produced 1,600 pounds of ice in 24 hours; and later discovered that ice would be trans parent, with the exception of a small porous core, if frozen at a temperature slightly below the freezing point. In 1857 Dr. Jahn Gorrie of Apalachicola, Fla., patented his ice-making machine; this was later followed by the com pressed-air machine of Dr. Alexander Kirk; in 1858-60 the machine, upon which the modern ammonia absorption system was founded, was brought forth by Ferdinand P. E. Carre; and later the plate-ice system was introduced by Capt. David Smith of Chatham, Mass., who erected the first machine of this character in the United States at Oakland, Cal. There have been nearly 4,500 patents taken out in the United States alone for refrigeration processes.