36 



REPORT 1865. 



The number of ballfuls required to produce the precipitate being counted, on re- 

 ferring to the Table the percenttige of carbonic acid in the air is at once seen. An 

 easy method of finding the precipitate for comparison is by shaking half an ounce 

 (14-17 cub. centims.) of baryta- water in a bottle with 23 ounces of Manchester air, 

 or nearly 30 ounces of London air (and elsewhere according to residence.) 



Experiments made with this apparatus show it to be extremely delicate. The 

 carbonic acid in the air of a room can be estimated in a few minutes. For very 

 bad air smaller balls are used, but in all cases only half an ounce of baryta-water. 



The second way of using the miuimetric method was partly described in the re- 

 port on the air of mines, and long tables were there given both for baryta- and lime- 

 water. It is more particularly adapted for use in houses and workshops. 



Suppose we desire to know if the air contains more than 0-04 per cent, carbonic 

 acid, we fill a bottle containing 5-422 ounces with air, by pumping or otherwise, 

 and shake in it half an ounce of baryta-water. If there is any precipitate at all, 

 the amount of carbonic acid in the air is above 0-04 per cent. This woidd indicate 

 that the air is less pure than outside. 



If we allow 0-0G per cent, of carbonic acid in a room, we take a bottle of the size 

 of 3-281+ J ounce=3-781 ounces (or 107-19 cub. centims.), and if after trial as above, 

 we tind a precipitate, however small, or even a slight milkiness, the air is deterio- 

 rated beyond 0-06. This relates to dwelling-houses. 



If for workshops we allow \ per cent. (0-25), a bottle of 0-788+ J ounce = 1-288 

 ounces (or 36-51 cub. centims.) is sufficient. 



If | per cent, is allowed (0-50), a bottle of 0-394 + i ounce =0-894 ounce (or 

 25-34 cub. centims.) is enough. 



Both of these two last sizes of bottles are small enough to be carried in the 

 waistcoat pocket. The addition of the 5 ounca is for the space occupied by the 

 baryta-water. 



Lime-water, being very common, will probably be often substituted for baryta- 

 water. The experiment is exactly the same, only larger bottles are required. 



- 06 per cent, carbonic acid in the air gives no precipitate or milkiness when 

 ^ an ounce of lime-water is shaken in a bottle of air containing 10-567 ounces 

 ( = 299-57 cub. centims.). 



0-25 per cent, carbonic acid in the air gives no precipitate or milkiness when 

 \ an ounce of lime-water is shaken in a bottle of air, containing 2-916 ounces 

 (=82-67 cub. centims.). 



0-50 per cent, carbonic acid in the air gives no precipitate or milkiness when 

 I an ounce of lime-water is shaken in a bottle of air containing 1-708 ounce 

 (=48-42 cub. centims.). 



