PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 389 



and labor at $1.25 per day, an establishment making fifty tons 

 per day, would make the ice for $2.50 per ton. It costs the 

 merchant Avho buys at retail about $13 a ton at New Orleans. 

 At San Francisco, large cargoes are brought from Sitka sound, 

 and sold at $40 to $100 per ton. Boston ice cannot be carried 

 there for $60 per ton. In Australia it is worth $100 per ton ; 

 and frequently cannot be obt.-^ined there at all. 



Mr. Leslie exhibited a model of Bartlett's Polar Refrigerator. 

 It has a central ice chamber of a wedge shape, the point being 

 downwards. . The sides of the ice chamber are of corrugated 

 metal, on which the moisture in the provision chambers is con- 

 densed, causing the confined air to be dry. 



The Chairman suggested the importance of well arranged 

 experiments with the different refrigerators in the market, to 

 determine practically what are their comparative merits. Sellers 

 of refrigerators generally represent that a less quantity of 

 ice is necessary than families find to be so, in practical use. 



Mr. Dibben considered ventilation as important as keeping 

 cold or keeping dry, to get rid of the putrefying gases. 



Dr. Yanderweyde stated that for every pound of moisture con- 

 densed, seventeen pounds of ice must be melted. It is therefore 

 important in conducting experiments to note the humidity of 

 the atmosphere. The soluble .gases will pass off merely from 

 the condensation of the moisture of the air, and the removal of 

 the condensed moisture ; but there are other gases arising from 

 decay which are insoluble and which will remain unless there is 

 ventilation. 



Subject for discussion. — The subject selected for discussion at 

 the next meeting, was, " Cooking and portable apparatus for 

 cooking." Adjourned. 



American Institute, Polytechnic Association, 



June 13, 18G1. 

 Mr. Jireh Bull in the chair. 



copper-plate printing by machinery. 

 Mr. Johnson exhibited specimens of steel-plate and copper- 

 plate engravings, printed by machinery. The plate is put upon 

 an endless belt passing horizontally over rollers. While inverted 

 it is first inked, and then the excess of ink is taken oft' by a felt 



