30 A RESPIRATION CALORIMETER. 



While the mixture is cooling the stirring is continued and the larger 

 lumps broken into smaller bits as much as possible. It is then trans- 

 ferred to a shallow pan and broken into small particles with a large 

 iron pestle. Before being used the material is sifted through wire 

 gauze with a mesh 4 mm. square, the larger particles being reduced by 

 means of a pestle to a size that will pass through the sieve. 



When properly made the soda lime is sufficiently moist to appear 

 distinctly damp, no dust being visible, and yet not so damp that it will 

 ' ' cake ' ' when being crushed with the pestle. In color it is white with 

 a slight yellowish tinge. The finished product is stored in galvanized- 

 iron ash-barrels with the top hermetically sealed by a tin cover waxed 

 at the edges. 



The caustic soda is purchased in cans varying in weight from 5 to 25 

 pounds, and as fast as a can is opened it is emptied into a large glass 

 jar, which can be tightly closed. The requisite quantity for each batch 

 is weighed out into a porcelain evaporating dish on scales weighing to 

 within one or two grams. As a matter of fact, the observance of the 

 exact proportions is not strictly necessary, and probably the weights 

 taken vary from 10 to 20 grams from those given above. 



The pulverized quicklime is best obtained by taking a barrel of the 

 best quality of fresh lime, pulverizing it with a pestle, and storing it 

 in an iron ash-barrel, which can be carefully closed at the top. The 

 lime in this condition is ready to be weighed and added directly to the 

 strong lye. It is important that the lime used be very fresh, and each 

 barrel should be tested to make sure that the material slacks freely. 



If the lime is not of standard strength, or if the proportions of the 

 soda and lime are not carefully maintained, the mixture is likely to be 

 too moist and form pasty lumps. In some instances it is possible to 

 utilize such a product by mixing with it some especially dry soda lime, 

 though as a rule the product would better be rejected and another lot 

 of lime used. With due precautions and care, however, the manufact- 

 ure proceeds smoothly and with minimum waste of material. A ton 

 or more of this soda lime has been made in this laboratory in the past 

 three years, and the method and finished product have been all that 

 could be desired. 



Efficiency of the carbon-dioxide absorbers. In the absorption of carbon 

 dioxide by soda lime the reaction may be considered as resulting in the 

 formation of calcium carbonate and sodium carbonate from calcium 

 oxide and sodium hydroxide. Assuming that the soda lime is a mix- 

 ture of equal parts by weight of sodium hydroxide and calcium oxide, 

 a soda-lime can containing 6 kilos of soda lime should, theoretically, 

 absorb not far from 4,000 grams of carbon dioxide. In practice, how- 



