128 Dr Bischof ' s Examination of Three Inflammable Gases 



The errors of measurement which occur when the inflamma- 

 ble gas and the oxygen are separately measured in each indi- 

 vidual experiment were thus likewise avoided. 



The detonation-tubes were graduated by myself with the 

 greatest care. The portions were so long, that each given 



ric air having replaced some of the gas in the bottle. This disadvantage- 

 ous action may, however, he counteracted by immersing the whole bottle 

 under water, and so removing the cork from contact with the atmospheric 

 air ; but I preferred repeating the detonations in different tubes rapidly 

 after one another. This mode of proceeding affords the most exact results. 

 From four to six detonation-tubes are kept ready in the mercurial appa- 

 ratus, and they are filled immediately after one another with the explosive 

 gas, which is driven out of the bottle by gentle heat. In this way a great 

 deal of time is saved ; and the analyses are performed under the same cir- 

 cumstances, thus affording results which harmonize as much as can be de- 

 sired. There are just two things that must be most particularly attended 

 to, viz. first, that, both before and after the detonation, the gas be not mea- 

 sured until no further changes in its volume can be remarked ; and, second, 

 that the potash be left long enough in contact with the gas. The neglect 

 of these two precautions is the source of most of the errors. An hour at 

 least is required ere the gas in the detonation-tube acquires the tempera- 

 ture of the atmospheric air, especially after the detonation, which heats 

 the »as considerably. As to the absorption of the carbonic acid, it is to 

 be remarked that the last portions of that gas are not fully absorbed for 

 some time. This is particularly the case when the gas is in a rarefied 

 state, as, for example, when the gas amounts to but a small quantity, and 

 the detonation-tube is long. Hence it is advisable to incline the tubes as 

 much as possible during the absorption of the carbonic acid. If the tube 

 be perpendicular, and should the mercury within be about 14 inches above 

 its level without, four or five days may elapse before the absorption can 

 be accomplished by means of hydrate of potash. Hence I prefer effecting 

 the absorption by solution of potash, which is allowed to asceud through 

 the mercury. If the detonation-tube is then taken out of the mercurial 

 apparatus, and placed in a vessel filled with water, the absorption takes 

 place very rapidly by means of a little agitation ; and the gas left behind 

 can be immediately measured. 



It is, as I have already remarked, very difficult to prepare detonation- 

 tubes which remain air-tight for several days. Hence we must not neglect 

 to prove these tubes before using them by filling them with mercury, and, 

 as in the case of a barometer, placing them in a mercurial apparatus with 

 their melted ends uppermost. If the mercury sinks after six or eight days, 

 the tubes can be improved by applying a small grain of sealing-wax, and 

 melting it on the platinum wire by a little heat. We must, however, again 

 prove the repaired tube before employing it, for the imperfect place is not 

 always closed the first time. 



The difficulty of inclosing a platinum wire quite tightly in a glass tube 



