66 



The principle upon which this cooling is based is the repeated evapora- 

 tion of a dilution of sulphurous acid and its renewed condensation. 



The diagram shows in transverse section the construction of the 

 machine. Round the hollow axle are fixed two balls O and R oi bronze 

 materiai. The axle is supported by two bearings S. The ball C turns 

 in a cooling water basin D, the baU i? in a reservoir E, which is filled with 

 a pickle dilution.' In the ball C a compressor is built in, which, when the 

 shaft is turning, is kept in a vertical position by a counterweight B, whilst 

 the piston is moved to and fro by means of eccentrics on the shaft. The 

 compressor-cylinder is revolvable round two taps, and so it can foUow the 

 osciUatirtg motioi;i of the pistoij. The machine is filled in the factory with 

 sulphur dioxide as a colfi medium and after this it is closed hermetically. 

 When the machine is brought into revolutionary motion the compressor 

 exhausts the sulphur dioxide ^as out of the ball R and presses it in the 

 condenser G, whose wall is cooled by the water from the main tap, so that 

 the sulphur dioxide condenses. 



FlGTJRB 2. 



By the difference in pressure that exists between the contents of the 

 balls, the liquid is forced back through a little pipe, within the hollow 

 shaft to the sphere R, the evaporator, and is quickly evaporated there. 

 The expansion of the gas cools the evaporator, which in its tiun cools 

 the brine in which it revolves. 



The compressor is built within a chamber in the centre of G, which 

 chamber is filled with oil, so that the moving parts are excellently lubri- 

 cated. The oil is gathered at the bottom of the condenser and is taken up 

 by the turning movement of the ball, in order to be brought back into 

 the compressor chamber by a receptacle. In this manner a very good 

 lubrication takes place, whilst the oil, in consequence of the closed con- 

 struction of the machine, cannot come into contact with the air, so that 

 oxidation of the oil by the oxygen in the air is prevented, and the oil 

 continually preserves its good quaUties. 



The incubators used for germinations at low temperatures consist 

 of spacious zinc double-walled cupboards, which are screened against 

 temperature changes by an insulation of two layers of air, one layer of 

 cement-asbestos, and finally a wooden covering (Figure 3). The inner 

 chamber of each of the two compartments of such aji incubator is 

 about three-tenths of a cubic metre and contains 24 loose perforated zinc 

 trays on which seed beds are placed. It also holds a zinc basin at the 



