248 RENEWAL OF THE AIR IN LIVING-ROOMS. 



ter, by stoves (a well-heated stove providing a ventilation of from 40 to 90 cubic 

 meters of air hourly). That this ventilation is sufficient is proved by the fact 

 that the amount of carbon dioxid in the room remains constant. When there is 

 a more considerable difference between the temperature in the room and that 

 outside (as in winter) , the ventilation is more than sufficient. 



If, however, the cubic space allotted to each inmate is too small, as in over- 

 crowded hospitals, narrow ship-quarters, etc., then the necessary change of air 

 must be provided for by means of contrivances for artificial ventilation. The 

 same must be done if noxious exhalations are given off by the sick. Above all, 

 however, it is to be noted that the natural ventilation through the pores of walls 

 is greatly limited if they be damp. At the same time, damp walls are prejudicial 

 to health by reason of their greater conduction of heat, and also because the germs 

 of infectious diseases can develop in them, as in moist ground generally. 



Ventilation may be accomplished either by aspiration, the exchange of air 

 being brought about by suction-power; or by pulsion, the fresh air being pumped 

 into the room. 



The carbon dioxid contained in the air of a living-room may be estimated 

 as follows: A baryta-solution is prepared, containing 10 grams of crystallized 

 barium hydrate and 0.5 gram of barium chlorid in i liter of water. A large, 

 dry, accurately graduated, 6-liter flask is filled with air from the room to be in- 

 vestigated, by blowing the air for some time down to the bottom of the flask by 

 means of a bellows. Then, by means of a pipet 100 cu. cm. of the baryta-solution are 

 allowed to run into the flask, naturally displacing 100 cu. cm. of the air. The 

 flask is then closed with a rubber cap, and is allowed to stand for two hours, 

 being shaken occasionally. In this way all the carbon dioxid is absorbed by the 

 baryta-solution. Then, 25 cu. cm. of the clear, supernatant fluid are withdrawn 

 into a medicine-bottle, and are titrated with a normal oxalic-acid solution from 

 a graduated buret, until a drop of the mixture, when placed upon turmeric paper, 

 does not form a brown stain, that is until the reaction is neutral. A few drops of 

 a' solution of 0.2 gram of rosolic acid in 100 cu. cm. of dilute alcohol may also be 

 added to the baryta-solution in the medicine-bottle, producing a red coloration. 

 When oxalic acid is added, the mixture is decolorized by the slightest excess of 

 this acid. To prepare the normal oxalic-acid solution, 2.8636 grams of pure, 

 crystallized, undecomposed oxalic acid, dried by having stood over concentrated 

 sulphuric acid under a glass bell- jar for four hours, are dissolved in i liter of water; 

 i cu. cm. of this solution is equivalent to i mgm. of carbon dioxid. The number of 

 cubic centimeters of acid-solution added to the baryta-solution is noted. Now, 

 25 cu. cm. of the original baryta-solution, with which nothing has been done, are 

 titrated in like manner with the normal acid-solution to the point of neutralization; 

 here also the amount of the acid-solution added is noted. By subtraction the 

 difference is found between the amounts of normal acid-solution added in both 

 titrations. Each cubic centimeter of this difference is equivalent to i mgm. of 

 carbon dioxid, and the resulting value must be multiplied by 4, in view of the 

 fact that only 25 cu. cm. of the 100 cu. cm. of baryta-solution were titrated. The 

 result gives the milligrams of carbon dioxid in six liters minus 100 cu. cm. of air. 



The milligrams of carbon dioxid thus determined are converted into cubic 

 centimeters by multiplying them by 0.508 (as 0.508 cu. cm. of carbon dioxid, at 

 o C. and 760 mm. of barometric pressure, weighs i mgm.). The volume of the 

 air is further reduced to o C. and 760 mm. of barometric pressure. This is done 



according to the formula V, = v - B , in which V, represents the re- 



760. (i + 0.003665.0 ' 



duced volume desired, V the volume of air taken in the flask for the experi- 

 ment, B the barometer-reading taken at the time of the experiment, and t the 

 temperature in the investigated room. By this reduction-procedure the results 

 can be obtained in percentages for possible comparisons. 



Example: Twenty-five cu. cm. of the baryta-solution are neutralized by means 

 of 24.6 cu. cm. of the oxalic-acid solution; 25 cu. cm. of the baryta-solution after 

 the absorption of carbon dioxid (taken from the experiment-flask) are neutralized 

 by means of only 21.5 cu. cm. of the oxalic-acid solution. The difference between 

 them, 24.6 21.5 =3.1, represents 3.1 mgm. of carbon dioxid, which have been 

 absorbed in the 25 cu. cm. of baryta-solution. Accordingly, there are contained 

 in the 100 cu. cm. of baryta-solution employed 12.4 mgm. of carbon dioxid 

 (4 X 3-i). If it be assumed that the large flask of air contains 4100 cu. cm., of 

 which 100 cu. cm. have been displaced by an equal volume of baryta-solution 

 that has been run in, so that there remains a volume of air equal to 4000 cu. cm.; 



