TABLE III.
| Temperat. | Vol. of air. | Utmost force of | Weight of 100 cubic inches of aqueous vapour. | |
|---|---|---|---|---|
| Aqueous vapour. | Ethereal vapour. | |||
| -28° | 420 | Inches of | Inches of | |
| -20 | 428 | Merc. | Merc. | |
| -10 | 438 | Grains. | ||
| 0 | 448 | .08 | ||
| 10 | 458 | .12 | ||
| 20 | 468 | .17 | ||
| 30 | 478 | .24 | ||
| 32° | 480 | .26 | 7.00 | .178 |
| 33 | 481 | .27 | 7.18 | .184 |
| 34 | 482 | .28 | 7.36 | .191 |
| 35 | 483 | .29 | 7.54 | .197 |
| 36 | 484 | .30 | 7.73 | .203 |
| 37 | 485 | .31 | 7.92 | .209 |
| 38 | 486 | .32 | 8.11 | .216 |
| 39 | 487 | .33 | 8.30 | .222 |
| 40 | 488 | .34 | 8.50 | .229 |
| 41 | 489 | .35 | 8.70 | .235 |
| 42 | 490 | .37 | 8.90 | .245 |
| 43 | 491 | .38 | 9.10 | .255 |
| 44 | 492 | .40 | 9.31 | .267 |
| 45 | 493 | .41 | 9.52 | .275 |
| 46 | 494 | .43 | 9.74 | .284 |
| 47 | 495 | .44 | 9.96 | .293 |
| 48 | 496 | .46 | 10.18 | .303 |
| 49 | 497 | .47 | 10.41 | .313 |
| 50 | 498 | .49 | 10.64 | .323 |
| 51 | 499 | .50 | 10.87 | .329 |
| 52 | 500 | .52 | 11.10 | .341 |
| 53 | 501 | .54 | 11.34 | .354 |
| 54 | 502 | .56 | 11.59 | .366 |
| 55 | 503 | .58 | 11.85 | .378 |
| 56 | 504 | .59 | 12.12 | .384 |
| 57 | 505 | .61 | 12.39 | .396 |
| 58 | 506 | .62 | 12.66 | .402 |
| 59 | 507 | .64 | 12.94 | .414 |
| 60 | 508 | .65 | 13.22 | .420 |
| 61 | 509 | .67 | 13.51 | .432 |
| 62 | 510 | .69 | 13.80 | .444 |
| 63 | 511 | .71 | 14.10 | .456 |
| 64 | 512 | .73 | 14.41 | .468 |
| 65 | 513 | .75 | 14.72 | .480 |
| 66 | 514 | .77 | 15.04 | .492 |
| 67 | 515 | .80 | 15.36 | .509 |
| 68 | 516 | .82 | 15.68 | .521 |
| 69 | 517 | .85 | 15.90 | .539 |
| 70 | 518 | .87 | 16.23 | .551 |
| 71 | 519 | .90 | 16.56 | .569 |
| 72 | 520 | .92 | 17.00 | .580 |
| 73 | 521 | .95 | 17.35 | .598 |
| 74 | 522 | .97 | 17.71 | .610 |
| 75 | 523 | 1.00 | 18.08 | .627 |
| 76 | 524 | 1.03 | 18.45 | .645 |
| 77 | 525 | 1.06 | 18.83 | .662 |
| 78 | 526 | 1.09 | 19.21 | .680 |
| 79 | 527 | 1.12 | 19.60 | .700 |
| 80 | 528 | 1.16 | 20.00 | .721 |
Applications of the above Table.
These tables will be found of great use in reducing volumes of air from one temperature or pressure to any other given one: also in determining the specific gravities of dry gases from experiments on those saturated with or containing given quantities of aqueous or other vapours.
As several writers, and some of considerable eminence, have given erroneous or imperfect formulæ on these subjects, more particularly with regard to the effect of aqueous vapour in modifying the weights and volumes of gases, it has been thought proper to subjoin the following precepts and examples for the use of those who are not sufficiently conversant in such calculations.
The 5th column of the above table, or weight of aqueous vapour, is new, and may therefore require explanation. Gay Lussac is considered the best authority in regard to the specific gravity of steam; but it would be well if his results were confirmed or corrected, as they are of importance. According to his experience, the specific gravities of common air and of pure aqueous vapour, of the same temperature and pressure, are as 8 to 5, or as 1 to .625. Now I assume that 100 cubic inches of common air, free from moisture, of the temperature 60° and the pressure of 30 inches of mercury, weigh 31 grains nearly. It is an extraordinary fact that philosophers are not agreed upon the absolute weight of a given volume of common air. Most authors now assume the weight of 100 inches = 30.5 grains, whilst according to my experience it is more than 31 grains. If common air be assumed 31 grains, steam would be 19⅜ grains for 100 cubic inches, at the same temperature and pressure, could it subsist; but as it cannot sustain that pressure at the temperature of 60° we must deduct according to the diminished pressure, the utmost force of steam at 60° being .65 parts of an inch of mercury, we have 30 inches ∶ 19⅜ grains ∷ .65 ∶ .420 grains = the weight of 100 cubic inches of aqueous vapour at 60° and pressure .65 parts of an inch; which is the number given above in the table. The like calculation is required for any other pressure: but in addition to this, there is to be an allowance for the temperature from the 2d column: Thus, let the weight of 100 cubic inches of steam at 32° be required. We have 30 inch. ∶ 19⅜ grs. ∷ .26 inch. ∶ .1679 grs.; the weight of 100 inches of steam at 60°; then if 480 ∶ 508 ∷ .1679 ∶ .178 grs. = weight of 100 cubic inches of steam at 32° and pressure .26 parts of an inch, the tabular number required.
Examples.
1. How many cubic inches of air at 60° are equivalent in weight to 100 cubic inches at 45°?
By the column headed volume of air we have this proportion, if 493 ∶ 508 ∷ 100 inch. ∶ 103.04 inches, the volume required.
2. How many cubic inches of air with the barometer at 30 inches height, are equal in weight to 100 cubic inches when the barometer stands at 28.9 inches?