These soaps were for a long time manufactured only in England, where the
process was kept a profound secret. They are now made every where.
Equal parts of tallow soap, made perfectly dry, and spirit of wine, are
to be put into a copper still, which is plunged in a water-bath, and
furnished with its capital and refrigeratory. The heat applied to effect
the solution should be as slight as possible, to avoid evaporating too
much of the alcohol. The solution being effected, must be suffered to
settle; and after a few hours’ repose, the clear supernatant liquid is
drawn off into tin frames, of the form desired for the cakes of soap.
These bars do not acquire their proper degree of transparency till after
a few weeks’ exposure to dry air. They are now planed, and subjected to
the proper mechanical treatment for making cakes of any form. The soap
is coloured with strong alcoholic solution of archil for the rose tint,
and of turmeric for the deep yellow. Transparent soaps, however pleasing
to the eye, are always of indifferent quality; they are never so
detergent as ordinary soaps, and they eventually acquire a disagreeable
smell.
+---------------------------+-----------+-----------+-----------+
| Soap charged with duty in | 1834. | 1835. | 1836. |
+---------------------------+-----------+-----------+-----------+
| | _lbs._ | _lbs._ | _lbs._ |
|Hard |144,344,043|143,806,207|146,539,210|
|Soft | 10,401,281| 12,103,109| 13,358,894|
| | | | |
|Amount of duty at 1-1/2_d._| | | |
|per lb. on hard soap | _£_902,150| _£_930,039| _£_915,861|
| do. at 1_d._ | | | |
| soft soap | 43,339| 50,429| 55,662|
+---------------------------+-----------+-----------+-----------+
SOAPSTONE; see STEATITE.
SODA, _Caustic soda_ (_Hydrate de soude_, Fr.; _Aetznatron_, Germ.); is
an alkaline substance, used in chemical researches, in bleaching, and in
the manufacture of soap. It is prepared by boiling a solution of
crystallized carbonate of soda in 4 or 5 parts of water, with half its
weight of recently slaked and sifted lime. At the end of half an hour,
the vessel of iron, porcelain, or preferably silver, may be removed from
the fire, and covered carefully, till the calcareous matter has settled
into a solid magma at the bottom. The clear supernatant lye may be then
decanted into bottles for use in the liquid state, or evaporated, out of
contact of air, till it assumes an oily appearance, then poured upon an
iron or marble slab, broken into pieces, and put up in phials secured
with greased stoppers or corks.
Caustic soda is a white brittle mass, of a fibrous texture, a specific
gravity of 1·536, melting at a heat under redness, having a most
corrosive taste and action upon animal matters, dissolving readily in
both water and alcohol, attracting carbonic acid when exposed to the
atmosphere, but hardly any water, and falling thereby into an
efflorescent carbonate; it forms soaps with tallow, oils, wax, rosin;
dissolves wool, hair, silk, horn, alumina, silica, sulphur, and some
metallic sulphurets. It consists of 77·66 soda, and 22·34 water. A
solution of caustic soda affords no precipitate with solution of
chloride of platinum, or tartaric acid, as a solution of caustic potash
never fails to do.
The following TABLE of the quantity of CAUSTIC SODA contained in LYES of
different densities, has been given by Richter:--
+-----+---------+
|Spec.| Soda |
|grav.|per cent.|
+-----+---------+
| 1·00| 0·00 |
| 1·02| 2·07 |
| 1·04| 4·02 |
| 1·06| 5·89 |
| 1·08| 7·69 |
| 1·10| 9·43 |
| 1·12| 11·10 |
| 1·14| 12·81 |
| 1·16| 14·73 |
| 1·18| 16·73 |
| 1·20| 18·71 |
| 1·22| 20·66 |
| 1·24| 22·58 |
| 1·26| 24·47 |
| 1·28| 26·33 |
| 1·30| 28·16 |
| 1·32| 29·96 |
| 1·34| 31·67 |
| 1·35| 32·40 |
| 1·36| 33·08 |
| 1·38| 34·41 |
+-----+---------+
Soda free from water, can be obtained only by the combustion of
_sodium_, which see.
SODA, CARBONATE OF (_Kohlensaures natron_, Germ.): is the soda of
commerce in various states, either crystallized, in lumps, or in a crude
powder called soda-ash. It exists in small quantities in certain mineral
waters; as, for example, in those of Seltzer, Seydschutz, Carlsbad, and
the volcanic springs of Iceland, especially the Geyser; it frequently
occurs as an efflorescence in slender needles upon damp walls, being
produced by the action of the lime upon the sea salt present in the
mortar. The mineral soda is the sesquicarbonate, to be afterwards
described.
Of manufactured soda, the variety most antiently known is barilla, the
incinerated ash of the _Salsola soda_. This plant is cultivated with
great care by the Spaniards, especially in the vicinity of Alicant. The
seed is sown in light low soils, which are embanked towards the sea
shore, and furnished with sluices, for admitting an occasional overflow
of salt water. When the plants are ripe, the crop is cut down and dried;
the seeds are rubbed out and preserved; the rest of the plant is burned
in rude furnaces, at a temperature just sufficient to cause the ashes to
enter into a state of semi-fusion, so as to concrete on cooling into
cellular masses moderately compact. The most valuable variety of this
article is called _sweet barilla_. It has a grayish-blue colour and gets
covered with a saline efflorescence when exposed for some time to the
air. It is hard and difficult to break; when applied to the tongue, it
excites a pungent alkaline taste.
I have analyzed many varieties of barilla. Their average quantity of
free or alkalimetrical soda, is about 17 per cent.; though several
contain only 14 parts in the hundred, and a few upwards of 20. This soda
is chiefly a carbonate, with a little sulphuret and sulphite; and is
mixed with sulphate and muriate of soda, carbonate of lime, vegetable
carbon, &c.
Another mode of manufacturing crude soda, is by burning sea-weed into
kelp. Formerly very large revenues were derived by the proprietors of
the shores of the Scottish islands and Highlands, from the incineration
of sea-weed by their tenants, who usually paid their rents in kelp; but
since the tax has been taken off salt, and the manufacture of a crude
soda from it has been generally established, the price of kelp has
fallen extremely low.
The crystals of soda-carbonate, as well as the soda-ash of British
commerce, are now made altogether by the decomposition of sea salt.