_Expansion of certain Liquids by being Heated from 32° to 212°._
+----------------------------+-----------------+----------+----------+
| | |Expansion |Expansion |
| Substances. | Authority. | in |in Vulgar |
| | |Decimals. |Fractions.|
+----------------------------+-----------------+----------+----------+
|Mercury, |Dulong and Petit.|0·01801800| 1/55·5 |
|do. in glass, | do. do. |0·01543200| 1/65 |
|Water, from its maximum | | | |
|density, |Kirwan. |0·04332 | 1/23 |
|Muriatic acid (sp. gr. | | | |
|1·137), |Dalton. |0·0600 | 1/17 |
|Nitric acid (sp. gr. 1·40), | do. |0·1100 | 1/9 |
|Sulphuric acid (sp. gr. | | | |
|1·85), | do. |0·0600 | 1/17 |
|Alcohol (to its boiling | | | |
|point)? | do. |0·1100 | 1/9 |
|Water, | do. |0·0460 | 1/22 |
|Water, saturated with common| | | |
|salt, | do. |0·0500 | 1/20 |
|Sulphuric ether (to its | | | |
|boiling point)? | do. |0·0700 | 1/14 |
|Fixed oils, | do. |0·0800 | 1/12·5 |
|Oil of turpentine, | do. |0·0700 | 1/14 |
+----------------------------+-----------------+----------+----------+
If the density of water at 39° be called 1·00000,
at 212° it becomes 0·9548,
and its volume has increased to 1·04734;
at 77° it becomes 0·9973587,
and its volume has increased to only 1·00265,
which, though one fourth of the whole range of temperature,
is only 1/18 of the total expansion.
Water at 60° F. has a specific gravity of 0·9991953,
and has increased in volume from 39° to 1·00008,
which is only about 1/58 of the total expansion to 212°, with 1/64 of
the total range of temperature.
All gases expand the same quantity by the same increase of temperature,
which from 32° to 212° Fahr. = 180°/480 = 3/8, or 100 volumes become
137·5. For each degree of Fahr. the expansion is 1/480.
When dry air is saturated with moisture, its bulk increases, and its
specific gravity diminishes, because aqueous vapour is less dense than
air, at like temperatures.
The following Table gives the multipliers to be employed for converting
one volume of moist gas at the several temperatures, into a volume of
dry gas.
+------------+-----------+
|Temperature.|Multiplier.|
+------------+-----------+
| 53° F. | 0·9870 |
| 54 | 0·9864 |
| 55 | 0·9858 |
| 56 | 0·9852 |
| 57 | 0·9846 |
| 58 | 0·9839 |
| 59 | 0·9833 |
| 60 | 0·9827 |
| 61 | 0·9820 |
| 62 | 0·9813 |
| 63 | 0·9806 |
| 64 | 0·9799 |
| 65 | 0·9793 |
| 66 | 0·9786 |
| 67 | 0·9779 |
| 68 | 0·9772 |
| 69 | 0·9765 |
| 70 | 0·9758 |
| 71 | 0·9751 |
| 72 | 0·9743 |
| 73 | 0·9735 |
+------------+-----------+
EXTRACTS. (_Extraits_, Fr.; _Extracten_, Germ.) The older apothecaries
used this term to designate the product of the evaporation of any
vegetable juice, infusion, or decoction; whether the latter two were
made with water, alcohol, or ether; whence arose the distinction of
aqueous, alcoholic, and ethereous extracts.
Fourcroy made many researches upon these preparations, and supposed that
they had all a common basis, which he called the _extractive_ principle.
But Chevreul and other chemists have since proved that this pretended
principle is a heterogeneous and very variable compound. By the term
_extract_ therefore is now meant merely the whole of the soluble matters
obtained from vegetables, reduced by careful evaporation to either a
pasty or solid consistence. The watery extracts, which are those most
commonly made, are as various as the vegetables which yield them; some
containing chiefly sugar or gum in great abundance, and are therefore
innocent or inert; while others contain very energetic impregnations.
The conduct of the evaporating heat is the capital point in the
preparation of extracts. They should be always prepared if possible from
the juice of the fresh plant, by subjecting its leaves or other
succulent part, to the action of a powerful screw or hydraulic press;
and the evaporation should be effected by the warmth of a water bath,
heated not beyond 100° or 120° F. Steam heat may perhaps be applied
advantageously in some cases, where it is not likely to decompose any of
the principles of the plant. But by far the best process for making
extracts is in vacuo, upon the principles explained in the article
EVAPORATION. It is much easier to fit up a proper apparatus of this
kind, than most practical men imagine. The vacuum may either be made
through the agency of steam, as there pointed out, or by means of an
air-pump. One powerful air-pump may form and maintain a good vacuum
under several receivers, placed upon the flat-ground flanges of so many
basins, each provided with a stop-cock at its side for exhaustion. The
air-less basin containing the juice being set on the shelf of a
water-bath, and exposed to a proper temperature, will furnish in a short
time, a large quantity of medicinal extract, possessing the properties
of the plant unimpaired.
For exceedingly delicate purposes, the concentration may be performed in
the cold, by placing saucers filled with the expressed juice over a
basin containing sulphuric acid, putting a glass receiver over them, and
exhausting its air.