1516. Carbonic acid gas.—­n and o = 0.1 of an inch:  A, B inductric positive, discharge nearly all at o, or negative:  A, B inductric negative, discharge nearly all at n, or negative.  Intervals = 0.8 of an inch:  A, B inductric positive, discharge mostly at o, or negative.  A, B inductric negative, discharge all at n, or negative.  In this case the negative had a decided advantage in facility of discharge.

1517.  Thus, if we may trust this form of experiment, the negative small ball has a decided advantage in facilitating disruptive discharge over the positive small ball in some gases, as in carbonic acid gas and coal gas (1399.), whilst in others that conclusion seems more doubtful; and in others, again, there seems a probability that the positive small ball may be superior.  All these results were obtained at very nearly the same pressure of the atmosphere.

* * * * *

1518.  I made some experiments in these gases whilst in the air jar (fig. 131.), as to the change from spark to brush, analogous to those in the open air already described (1486. 1487.).  I will give, in a Table, the results as to when brush began to appear mingled with the spark; but the after results were so varied, and the nature of the discharge in different gases so different, that to insert the results obtained without further investigation, would be of little use.  At intervals less than those expressed the discharge was always by spark.

_______________________________________________________

________________
|               |                           |                           |
|               |     Discharge between     |    Discharge between      |
|               |       balls B and D.      |      balls A and C.       |
|               |___________________________|___________________________|
|               |             |             |             |             |
|               | Small ball  | Small ball  | Large ball  | Large ball  |
|               | B inductric | B inductric | A inductric | A inductric |
|               |   pos.    |   neg.    |   pos.    |   neg.    |
|_______________|_____________|_____________|_____________|_

____________|
|               |             |             |             |             |
| Air           |     0.55    |    0.30     |    0.40     |     0.75    |
| Nitrogen      |     0.30    |    0.40     |    0.52     |     0.41    |
| Oxygen        |     0.70    |    0.30     |    0.45     |     0.82    |
| Hydrogen      |     0.20    |    0.10     |             |             |
| Coal gas      |     0.13    |    0.30     |    0.30     |     0.44    |
| Carbonic acid |     0.82    |    0.43     |    1.60     | {above 1.80;|
|               |             |             |             |   had not   |
|               |             |             |             |   space.)   |
|_______________|_____________|_____________|_____________|_

____________|

1519.  It is to be understood that sparks occurred at much higher intervals than these; the table only expresses that distance beneath which all discharge was as spark.  Some curious relations of the different gases to discharge are already discernible, but it would be useless to consider them until illustrated by further experiments.