APPARATUS AND METHODS USED IN THIS RESEARCH. 39 



water-absorbers. This latter feature has been found of advantage, 

 although the insertion of the safety trap (A) has prevented this. The 

 speed of the blower may easily be altered by a simple lamp resistance, 

 these blowers usually giving a suitable ventilation — not far from 35 liters 

 per minute — when rotating at the speed of 270 revolutions per minute. 

 Even with this rate of ventilation, it has been shown by careful experi- 

 menting, with a portable alcohol lamp placed in different parts of the 

 chamber, that there is no draft which would be noticed by the infant. 

 The fact that the relative humidity does not become unduly low is 

 further proof that the infant is sojourning in an atmosphere approxi- 

 mately normal. 



Acid trap. — To prevent the possibility of sucking strong sulphuric 

 acid into the delicate mechanism of the blower, an empty glass bottle 

 (A) is inserted into the series. While almost any form of bottle can 

 be used for this purpose, it has been convenient for us to employ an 

 empty reversed "Williams bottle." 



Water absorber. — The air leaving the respiration chamber contains a 

 large amount of water-vapor from the lungs and skin of the infant and 

 from the moisture of the incoming ventilating air-current. Before the 

 carbon dioxide produced by the infant is absorbed, it is important to 

 remove this water-vapor entirely from the air. The current is there- 

 fore first passed through two or more bottles containing concentrated 

 sulphuric acid. Usually one large-sized Williams bottle (B) is sufficient 

 to collect nearly all of the moisture, but this is followed by a second bottle 

 (C), which retains the last traces of water- vapor. 1 To facilitate the hand- 

 ling of the bottles and to prevent breakage, they are usually inclosed 

 in a small wire basket with a handle, by means of which they may be 

 suspended directly from a hook on the arm of the balance. When these 

 two Williams bottles are used, it is possible to retain the first bottle in 

 the circuit until the acid has so far accumulated as to render it liable 

 to be carried over mechanically into the second bottle. Indeed, 100 

 or 200 grams of water-vapor may be absorbed; it is fundamentally 

 important, however, to note that the second Williams bottle must not 

 increase in weight more than 15 grams before being renewed. As a 

 matter of experimental routine, it has been found advantageous to 

 replace the first Williams bottle each day with another which has 

 previously served in the quantitative absorption of carbon dioxide, 

 replacing these bottles with new ones every other day. The second 

 Williams bottle should be controlled by weighing every few days. 



Tubing and piping. — The Williams bottles, as well as the soda-lime 

 bottles for absorbing the carbon dioxide, are fitted with short lengths 

 of rubber tubing of good quality, to which are attached respectively 

 male and female parts of ordinary garden hose couplings of the standard 



x The Williams bottles are made for us in Berlin by the Vereinigte Fabriken f. Laboratoriums- 

 bedarf. 



