BY DR. 0. KATZ. 259 



As will be seen below, the ice is nearly always used soon after 

 it is made, so that the question as to the living contents of ice- 

 samples of various ages is only of subordinate significance. For 

 the sake of uniformity I always analysed the ice-samples when 

 they were fresh, no more than about one day old. 



There ai'e at the present time thi'ee local ice-manufacturing 

 companies. 



(1) The above-mentioned "New South Wales Fresh Food and 

 Ice Company," Hai'bour-street. To Mr. W. G. Lock, Manager of 

 this Company, I am indebted for the following information which 

 I am permitted to give verbatim.* " The water used by this com- 

 pany for the manufacture of ice is that supplied to the City and 

 Suburbs of Sydney, but previous to being thus employed it is 

 carefully filtered, first through, a quantity of compressed sponges 

 and then through beds of animal charcoal. The ice is generally 

 supplied to customers as soon as manufactured, but on account of 

 the irregularity of the trade, and the necessity of not being 

 entirely dependent on the working of the machines for the extra 

 quantities of ice required daring the hottest weather, a stock of 

 some 400 or 500 tons is accumulated during the winter months 

 which gradually diminishes during the summer, so that occasionally 

 the ice sent out has been stored here for some three to nine 

 mouths. Our avex'age weekly sale is about 120 tons, so that the 

 quantity distributed of ice that has been kept is a very small 

 proportion. The principle of preparing the ice may be thus 

 described. The w^ater must be frozen from cells formed of two 

 vertical plates placed equidistant in a large tank containing the 

 filtei-ed water ; these cells have a hollow space in them through 

 which the refrigerating medium is made to flow, the water in the 

 tank is gradually frozen from the cells outwards, until the ice has 

 attained a thickness of from four to five inches when the liquid 

 circulating through the cells is heated, the ice released from them, 

 hoisted, and cut up by machinery. By this method of freezing 

 from one side of the plate only and never allowing the formation 



*I have also to acknowledge with thanks his liberality in providing all 

 the ice re(]uire<l gratis. 



