The following example is quoted:
Weight of the tin received, with its contained |
carbide . . . . . ._| = 6325 grammes.
Weight of the empty tin . . . . = 1485 "
_______
Carbide used . . . = 4840 " = 10670 lb.
The carbide in question was distributed among the nine receptacles and gasified. The readings were:
________________________________________________
| | | | |
| No. | Litres. | Degrees C. | Millimetres. |
|______|__________|______________|_______________|
| | | | |
| 1 | 152.5 | 13 | 762 |
| 2 | 136.6 | " | " |
| 3 | 138.5 | " | " |
| 4 | 161.0 | " | " |
| 5 | 131.0 | " | " |
| 6 | 182.5 | 13.5 | " |
| 7 | 146.0 | " | " |
| 8 | 163.0 | 14.0 | " |
| 9 | 178.5 | " | " |
|______|__________|______________|_______________|
After two hours, the total of the readings was 1395.0 litres at 13.5° C. and 762 mm., which is equivalent to 1403.7 litres (= 49.57 cubic feet) at 15° C. and 760 mm. (or 60° F. and 30 inches; there is no appreciable change of volume of a gas when the conditions under which it is measured are altered from 15° C. and 760 mm. to 60° F. and 30 inches, or vice versâ).
The yield of gas from this sample is therefore 1403.7/4.840 = 290 litres at 15° C. and 760 mm. per kilogramme, or 49.57/10.67 = 4.65 cubic feet at 60° F. and 30 inches per pound of carbide. The apparatus described can, of course, be used when smaller samples of carbide only are available for gasification, but the results will be less trustworthy if much smaller quantities than those named are taken for the test.
Other forms of carbide-to-water apparatus may of course be devised, which will equally well fulfil the requisite conditions for the test, viz., complete decomposition of the whole of the carbide without excessive rise of temperature, and no loss of gas by solution or otherwise.
An experimental wet gas-motor, of which the water-line has been accurately set (by means of the Gas Referees' 1/12 cubic foot measure, or a similar meter-proving apparatus), may be used in place of the graduated gasholder for measuring the volume of the gas evolved, provided the rate of flow of the gas does not exceed 1/6 cubic foot, or say 5 litres per minute. If the generation of gas is irregular, as when an apparatus of the type described above is used, it is advisable to insert a small gasholder or large bell-governor between the washer and the meter. The meter must be provided with a thermometer, according to the indications of which the observed volumes must be corrected to the corresponding volume at normal temperature.
If apparatus such as that described above is not available, fairly trustworthy results for practical purposes may be obtained by the decomposition of smaller samples in the manner described below, provided these samples are representative of the average composition of the larger sample or bulk, and a number of tests are made in succession and the results of individual tests do not differ by more than 10 litres of gas per kilogramme (or 0.16 cubic foot per pound) of carbide.
It is necessary at the outset to reduce large lumps of carbide in the sample to small pieces, and this must be done with as little exposure as possible to the (moist) air. Failing a good pulverising machine of the coffee-mill or similar type, which does its work quickly, the lumps must be broken as rapidly as possible in a dry iron mortar, which may with advantage be fitted with a leather or india-rubber cover, through a hole in which the pestle passes. As little actual dust as possible should be made during pulverisation. The decomposition of the carbide is best effected by dropping it into water and measuring the volume of gas evolved with the precautions usually practised in gas analysis. An example of one of the methods of procedure described by the German Association will show how this test can be satisfactorily carried out: