386 



THE AIR OF TOWNS. 



attacked by a wild beast we do not remain passive. We prepare to kill 

 it or to run away. And if the health of a town population is slowly 

 undermined, as it assuredly is, by causes which we can compass and 

 prevent, as we can not run away to pure air, we must face those causes 

 and stamp them out. There is much that the local authority can and 

 ought to do, and which we should collectively see is done. But there 

 is much that we as individuals can do ourselves. It is a duty to our- 

 selves that these things should be done. It is equally a duty to the 

 young and growing generation. 



appendix i . 



A RAPID METHOD FOR 



THE ESTIMATION OF CARBONIC ACID IN 

 THE AIR. 



£30 



Fig. l. 



(1) A standard solution of limewater.— Pure water is left in contact with slacked 

 lime until saturated. The clear decanted liquid is diluted with ninety-nine times 

 its volume of distilled water. Make 1 quart or 1 liter. 



(2) Phenolphthalein solution is made by dissolving one part of phenolphthalein in 

 five hundred times its weight of dilute alcohol [equal volumes of pure alcohol and 



water]. Make 3 ounces or 100 cubic centimeters. 

 ^J~^-~ (3) A 20-ounce stoppered oottle with (preferably) a hollow stopper 



marked to hold 3 drams or 10 cubic centimeters. 



A sample of air is taken by blowing air into the clean stoppered 

 bottle (fig. 1) with bellows. Six minims or one-third of a cubic cen- 

 timeter of the phenolphthalein solution is then added, and the meas- 

 ured volume of limewater is run into the hollow stopper. 

 The limewater is poured into the bottle, the stopper inserted, the time noted, and 

 the contents vigorously shaken. If the red color of the liquid disappears in three 

 minutes or less the atmosphere is unfit for respiration. 



The stock of limewater should be kept in a bottle,(fig. 2) fur- 

 nished with a tap and coated within with a film of paraffin, and 

 iu the neck an open tube should be inserted containing pieces of 

 caustic soda or quicklime. The phenolphthalein solution is best 

 measured by means of a narrow glass tube passing through the 

 cork of the bottle upon which the measured volume is marked. 

 If the cork fits easily the liquid may be forced up exactly to the 

 mark by pushing in the cork. 



The following are estimations made in this manner compared with the results 

 obtained by Pettenkofer's method : 



Fig. 



Time. 



Per cent vol- 

 ume of car- 

 bonic acid. 



Minutes. 





14 



0. 1618 



i§ 



.1379 



11 



.1279 



H 



. 07716 



4i 



. 05142 



5 



.0464 



71 



.0351 



