TIIKHMAI. PBOPEBTBB OF CAl.T.ONir ACID AT LOW TEMPERATURES. (i 



l'Y.>in the results of these six sets of experiments all* the data were calculated for 

 constructing the fy> diagram ('mm +20 C. to 50 C. The diagram is shown in 

 fig. 12, p. 79, and some of the results are given in Table IX. 



Tin- experiments WIT.- i-.m iud mil in tin- Kngineerinjr I,alx>ratory at Oxford with a 

 vapour- compression free/ing machine, presented to the Laboratory by BrasenoM 

 College. In addition to the usual parts the apparatus includes a pair of suspended 

 flasks by \\liii-li the rate of flow of the CO., round the circuit can be measured. The 

 following additional apparatus was made for these experiments: Two electrically 

 heated calorimeters, one of which always replaced the refrigerating tank of the 

 free/ing machine; several thermo-junctions for measuring the temperatures of the 

 calorimeters and of the CO, at various points in the circuit ; a graduated glass 

 capillary tul>e, with regulating valves, for measuring the changes of volume of liquid 

 ( K ) 3 under varying pressures and temperatures in Series V. experiments ; and a 

 s|ie.-i:d throttle- valve for Series IV. 



The gas used was commercial CO 2 , supplied by Messrs. Barrett and Elers, Limited, 

 of London, who have kindly informed the authors how it is made. Coke is burnt in 

 a furnace and the products of combustion, after being washed with hot and cold 

 water in scrubbers filled with fragments of limestone to eliminate any SO 3 , are passed 

 through absorbing towers filled with coke over which a stream of potash lye flows 

 which absorbs the CO.,. The enriched lye is then heated in iron boilers and the CO,, 

 driven off by the heat, is compressed in compound pumps into the steel flasks in 

 which it is sold. It is dried by passing over calcium chloride between the first and 

 second stage of compression. The gas made in this way is said by the makers to 

 contain no impurities, except possibly per cent, to per cent, of air and traces 

 of SO a . These traces of S0 2 were probably eliminated with the moisture in the 

 special drying appliances used in these experiments, so that the oidy impurity left 

 was air. 



To estimate the amount of air present the gas was analysed in a modified form of 

 HKMPEL'S apparatus specially arranged for this test. About 100 c.c. of gas was 

 measured over mercury in a burette and then passed into the potash absorption bulb. 

 The residue of undissolved gas (air) was then drawn back into a small burette and 

 measured over potash solution. The apparatus was arranged so that the test could 

 ! repeated as often as desired while the residue accumulated in the small burette. 

 In this way a sufficient quantity could lx- analysed to allow of an accurate deter- 

 mination of the small amount of air. The amount of air found was only O'll per 

 cent, by volume ('073 per cent, by weight). ANDREWS,! in his classical experiments, 

 never was able to reduce the air in the gas he used to less than B oo t ro l oo- The 



h This is not strictly accurate. In working out Series V. the density of liquid CO... at one temperature 

 is needed. BEIIN'S result has IHJCII used. Any possible error in thia has no appreciable effect on the 

 result. With this exception every quantity needed has been measured. 



t '1'hil. Trans.,' 18G9, p. 381. 



