108 



VETERINARY HYGIENE 



The Lunge-Zeckendorff Method. This is a more accurate 

 method than the former, and requires more careful attention to 

 details. As air containing an appreciable amount of CO 2 is acid 

 to phenolphthalein, it follows that if it is passed through a slightly 

 alkaline medium it will tend to neutralise the alkalinity, and if a 

 standard alkaline solution be used and coloured by phenolphthalein 

 and the amount of air passed through measured, it is possible to 

 calculate the exact amount of carbonic acid gas in the air. The 

 method is as follows : The apparatus consists of a 70 c.c. flask 

 fitted with a rubber stopper and two tubes as in a wash bottle, and 

 an indiarubber valve pump of 70 c.c. capacity. Make a N/10 

 sodium carbonate solution, 5-3 grammes per litre, and colour with 

 phenolphthalein; from this solution make the working solution by 

 taking 2 c.c. of the above and making up to 100 c.c. with distilled 

 water, boil, cool and make up to the 100 c.c. mark with distilled 

 water. This solution will not keep, and must be freshly made on 

 the day it has to be used. For each estimation take 10 c.c. of 

 the working solution, place it in a flask, and at the place where 

 you wish to examine the air slowly compress the rubber ball between 

 the palms of the hands and force the air through the solution. 

 Shake the bottle well and allow the pump to re-fill with air. Repeat 

 this operation until the phenolphthalein is decolourised. The 

 Na 2 CO 3 is converted into the bi-carbonate by the CO 2 of the air 

 thus : 



Immediately there is excess of CO 2 the colour of the phenolph- 

 thalein is discharged. The number of times the ball has to be 

 squeezed gives the amount of CO 2 as shown hereunder : 



With Pettenkofrer's method the reduction in the alkalinity of 

 a fluid caused by passing through it air containing CO 2 is measured 

 by the use of a standard solution of oxalic acid. 



Examination of the Air for P articulate Bodies. This may be 

 done by exposing a series of slides, moistened with glycerine, in 

 different parts of the building ; the glycerine should cover a definite 

 area of the slide, say 1 square inch, and the time of exposure should 



