THE PRICE OF ANESTHESIA 619 



attempted to devise a ready method of delivering chloroform 

 vapour and air between the required limits. 



I have at last hit upon a combined method of estimation and 

 of delivery that has proved itself to be an admirable laboratory 

 method, and that will, I believe, prove to be of great service as 

 a hospital method of exact administration. 



The arithmetical data upon which the method depends are 

 as follows : 



A litre of chloroform vapour weighs . 53 grammes 



Difference .... 40 ,, 



Or difference per i c.c. . 4*0 milligrammes 

 A litre of chloroform and air at i per cent., or 990 c.c. of 

 air+io c.c. CHCI3, weighs r34 grammes, and every 40 milli- 

 grammes of weight in a litre flask or bulb of mixture 

 indicates i per cent, of chloroform vapour in the mixture — 

 or in a 250 c.c. bulb each centigramme indicates i per cent. 

 This affords a ready means of estimating from time to time 

 the percentage of chloroform vapour in mixtures of chloro- 

 form and air, and I have used it extensively as a means of 

 calibration and control of apparatus. But, obviousl}-, it is not a 

 method for use outside the laboratory. 



But the next step, by which I sought to obtain for the 

 laboratory a means of estimating from moment to moment, and 

 recording, the fluctuations of percentage taking place in the 

 chloroform mixture delivered to an animal, and of var3'ing the 

 percentage as desired for the experiment, put me in possession 

 of an instrument which at once fulfilled its laboratory purpose 

 and at the same time is obviously capable of being transferred 

 to the operating theatre. 



Instead of weighing in air a bulb full of chloroform mixture, 

 I weighed, or rather counterpoised, a bulb full of air in a jar 

 traversed by the chloroform mixture ; the bulb, of course, rose 

 and fell as the mixture was made more or less dense by more 

 or less chloroform vapour. The pointer of the balance was then 

 graduated in chloroform percentages by appropriate weights — 

 increments of 40, 80, 120 milligrammes for i, 2, and 3 per cent. 

 CHCI3 with a litre bulb.^ A light pen fixed to the beam of the 



^ I have not talked about temperature and pressure corrections, which should 

 be taken into account when required, and ignored when not required. For 



