give the rates of carbonic acid in the quantity of air which will produce no precipitate in half an ounce of lime water. Column 3 is the same as column 2; but 14·16 c. c. (half an ounce) is added to give the corresponding size of the bottle, and column 4 gives the size of the bottle in ounces.
To be used when the point of observation is “no precipitate.” Half an ounce of baryta water contains about ·08 gramme of baryta.
Air at 0° C. and 760 millims. Bar.
| Carbonic Acid in the Air, per cent. | Volume of Air in cubic centimètres. | Size of bottle in cubic centimètres. | Size of bottle in ounces Avoirdupois. |
| ·03 | 185 | 199 | 7·06 |
| ·04 | 139 | 154 | 5·42 |
| ·05 | 111 | 125 | 4·44 |
| ·06 | 93 | 107 | 3·78 |
| ·07 | 79 | 93 | 3·31 |
| ·08 | 70 | 84 | 2·96 |
| ·09 | 62 | 76 | 2·69 |
| ·10 | 56 | 70 | 2·46 |
| ·11 | 51 | 65 | 2·29 |
| ·12 | 46 | 60 | 2·14 |
| ·13 | 43 | 57 | 2·01 |
| ·14 | 40 | 54 | 1·90 |
| ·15 | 37 | 51 | 1·81 |
| ·20 | 28 | 42 | 1·48 |
| ·25 | 22 | 36 | 1·29 |
| ·30 | 19 | 33 | 1·16 |
| ·40 | 14 | 28 | 1·04 |
| ·50 | 11 | 25 | ·89 |
| ·60 | 9 | 23 | ·89 |
| ·70 | 8 | 22 | ·78 |
| ·80 | 6 | 20 | ·72 |
| 1·00 | 5·5 | 19·7 | ·70 |
Mr Wanklyn’s process for the determination of carbonic acid in the atmosphere is as follows:—A solution of carbonate of soda is first made as follows: 4·47 grammes of gently-ignited carbonate of soda are dissolved in one litre of water, giving a solution of such a strength that 1 c. c. contains exactly 1 c. c. of carbonic acid (= 1·97 milligrammes of CO2); a large quantity of baryta water (strength about 0·1 per cent.) is prepared.
If now 100 c. c. of clear baryta water be treated with 1 c. c. of carbonate of soda, just described, a certain degree of turbidity is produced.
If 2 c. c. of the solution be taken another degree of turbidity is produced, and so on. If, then, a bottle capable of holding 2000 c. c. of air, together with 100 c. c. of baryta water, be filled with the sample of air to be tested, there will be a certain depth of turbidity produced by shaking it up. Having got the air to expend itself on 100 c. c. of baryta water the degree is to be found by comparison with another 100 c. c. of baryta water, in which a like turbidity has been induced by means of the standard solution of carbonate.
Every c. c. of soda solution counts for a c. c. of carbonic acid in two litres of air. A consumption of 1 c. c. will correspond to ·05 volumes of carbonic acid per cent. Good air should accordingly not take more than 1 c. c. of soda solution, air which takes already 2 c. c. being already bad.
In order practically to carry out this method of estimating carbonic acid the following apparatus is required:—Several bottles capable of holding 2·210 c. c., and well stoppered (failing bottles of exactly the right capacity Winchester quart bottles will answer); a small pair of bellows; several colourless glass cylinders marked at 100 c. c. capacity—the Nesslerising cylinders will answer for this purpose—a graduated pipette or burette to deliver tenths of a c. c. of solution, the standard solution of carbonate of soda, and the baryta water, which may be of moderate strength.
The testing is managed thus: Winchester quart bottles having been made clean are rinsed with distilled water, and allowed to drain a little. They are then closed with their stoppers, and are ready for use. The operator having provided himself with two or three of these bottles and a small pair of bellows enters the room the air of which is to be tested. The stopper is then removed from one of the bottles, and some air of the room blown through with the bellows, and then the stopper is replaced, and the bottle carried away to be tested.
The testing is done by pouring into the bottle 100 c. c. of clear baryta water, shaking up for two or three minutes, and then pouring out into a cylinder of colourless glass, and observing the depth of the turbidity in various lights and against various backgrounds. The turbidity is to be exactly imitated by means of the standard solution of carbonate of soda. In order to imitate the turbidity produced by a Winchester quart full of good air only 1 c. c. of this solution of carbonate of soda is required.