The following table, due to Mr W.D.  Field, shows very plainly the great variation in the time of the immersion and the temperature by seemingly very slight causes.  It extends over fourteen working days, during which time it rained four days.  The formula used is that given above, except that the specific gravity of the nitric acid is somewhat lower.  The product obtained differs only from that produced by using nitric acid of specific gravity 1.43 in being soluble in methyl-alcohol.  From 30 to 35 lbs. of pyroxyline were produced in each of the fourteen days.

A careful examination of this table will prove very instructive.  The increase in yield varies from 31 per cent. to nothing, and the loss runs as high as 10 per cent., yet care was taken to make the product uniform in quality.  On the days it rained there was a loss, with the exception of the fourth day, when there was neither a loss nor a gain.  On the days it was partly clear, as just before or after rain, the table shows a loss in product.  We can explain this fact by reason of the moisture-absorbing qualities of the cotton.  On the rainy days it would absorb the moisture from the air until, when immersed in the acids, they were weakened, and the fibre dissolved more or less in weakened acid, producing what is known as “burning” in the batch.  It will also be noticed that on days which show a loss, the time of the immersion was correspondingly short, as on the a loss, the time of the immersion was correspondingly short, as on the tenth, twelfth, and seventh days.

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_______________
|                |                     |                               |
|                |  Specific Gravity.  |               Time.           |
|                |_____________________|_______________________________|
|                |            |        |      |        |      |        |
|                |H_{2}S0_{4}.|HNO_{3}.|Hours.|Minutes.|Hours.|Minutes.|
|________________|____________|________|______|________|____

__|________|
|                |            |        |      |        |      |        |
| 1.  Clear       |   1.838    | 1.4249 |  ... |   20   |  4   |   ...  |
| 2.   "         |   1.837    | 1.4249 |  ... |   20   |  2   |   ...  |
| 3.  Cloudy      |   1.837    | 1.4226 |  ... |   45   |  2   |   ...  |
| 4.  Rain        |   1.837    | 1.420  |  ... |   20   |  1   |   20   |
| 5.  Clear       |   1.8377   | 1.42   |  1   |   15   |  2   |   ...  |
| 6.  Rainy       |   1.8391   | 1.422  |  ... |   35   |  1   |   40   |
| 7.  Cloudy      |   1.835    | 1.4226 |  ... |   20   |  ... |   35   |
| 8.  Clear       |   1.835    | 1.422  |  ... |   35   |  1   |   10   |
| 9.  Partly Clear|   1.824    | 1.4271 |  ... |   20   |  1   |   ...  |
|10.     "       |   1.83     | 1.4271 |  ... |   10   |  ... |   25   |
|11.  Cloudy      |   1.832    | 1.425  |  ... |   10   |  ... |   50   |
|12.  Rainy       |   1.822    | 1.425  |  ... |   10   |  ... |   20   |