58 CALORIMETERS FOR STUDYING RESPIRATORY EXCHANGE, ETC. 



positive blower and capable of producing at the outlet considerable pressure 

 and at the inlet a vacuum of several inches of mercury. At a speed of 230 

 revolutions per minute it delivers the air at a pressure of 43 millimeters of 

 mercury, forcing it through the purifying vessels at the rate of 75 liters 

 per minute. This rate of ventilation has been established as being satis- 

 factory for all experiments and is constant. Under the pressure of 43 mil- 

 limeters of mercury there are possibilities of leakage of air from the blower 

 connections and hence, to note this immediately, the blower system is 

 immersed in a tank filled with heavy lubricating oil. The connections are so 

 well made, however, that leakage rarely occurs, and, when it does, a slight 

 tightening of the stuffing-box on the shaft makes the apparatus tight again. 



ABSORBERS FOR WATER-VAPOR. 



To absorb 25 to 40 grams of water-vapor in an hour from a current of air 

 moving at the rate of 75 liters per minute and leaving the air essentially 

 dry under these conditions has been met by the apparatus herewith described. 

 The earlier attempts to secure this result involved the use of enameled- 

 iron soup-stock pots, fitted with special enameled-iron covers and closed 

 with rubber gaskets. For the preliminary experimenting and for a few 

 experiments with man these proved satisfactory, but in spite of their 

 resistance to the action of sulphuric acid, it was found that they were not 

 as desirable as they should be for continued experimenting from year to 

 year. Eecourse was then had to a special form of chemical pottery, glazed, 

 and a type that usually gives excellent satisfaction in manufacturing con- 

 cerns was used. 



This special form of absorbers presented many difficulties in construc- 

 tion, but the mechanical difficulties were overcome by the potter's skill and 

 a number of such vessels were furnished by the Charles Graham Chemical 

 Pottery Works. Here again these vessels served our purpose for several 

 months, but unfortunately the glaze used did not suffice to cover them com- 

 pletely and there was a slight, though persistent, leakage of sulphuric acid 

 through the porous walls. To overcome this difficulty the interior of the 

 vessels was coated with hot paraffin after a long-continued washing to remove 

 the acid and after they had been allowed to dry thoroughly. The paraffin- 

 treated absorbers continued to give satisfaction, but it was soon seen that 

 for permanent use something more satisfactory must be had. After innu- 

 merable trials with glazed vessels of different kinds of pottery and glass, 

 arrangements were made with the Royal Berlin Porcelain Works to mold 

 and make these absorbers out of their highly resistant porcelain. The result 

 thus far leaves nothing to be desired as a vessel for this purpose. A number 

 of such absorbers were made and have been constantly used for a year and 

 are absolutely without criticism. 



