Cooley's Cyclopaedia of Practical Receipts Volume Ii Part 236

These effects are due to the formation on the surface of the steel of films of oxide of different degrees of thickness, and to the action of the light on these. They are precisely a.n.a.logous to those which are caused when a ray of reflected light falls upon any other body, the surface of which is composed of thin layers, which are continually changing in thickness, such as a soap-bubble, or a thin coating of tar or oil swimming on water, and which are exemplified in Newton's rings.

As each shade of colour is an index of the temperature of the steel, and as this determines its adaptability for various purposes, all that the workman has to do, when he requires it for any special object, is to heat it by the proper methods (such as a bath of oil, or tallow, or melted metal) until it acquires the desired colour, and then to allow it to gradually cool.

The following table, exhibiting the different melting points of steel when employed in the manufacture of different kinds of works, together with the corresponding colours, the composition of the metallic baths, &c., is from Dr Wagner's 'Handbook of Chemical Technology,' edited by W. Crookes, Esq., F.R.S.

Composition of Metallic Mixture.

__________ Melting Lead. Tin. Point. Temperature.

Lancets 7 4 220 C Hardly pale yellow.

Razors 8 4 228 " Pale yellow to straw yellow.

Penknives 8-1/2 4 232 " Straw yellow.

Pairs of scissors 14 4 254 " Brown.

Clasp-knives, joiners' and } 19 4 265 " Purplish colour.

carpenters' tools } Swords, cutla.s.ses, watch- } 48 4 288 " Bright blue.

springs } Stilettos, boring tools, and} 50 2 292 " Deep blue.

fine saws } Ordinary saws {in boiling linseed} {oil } 316 " Blackish blue.

Steel is of a greyish-white colour, and has a sp. gr. varying from 766 to 793. During hardening the sp. gr. becomes reduced from 793 to 766, whilst it experiences a slight increase of volume. The property (already pointed out) that steel possesses of becoming hard after being heated to redness, and suddenly chilled, does not belong to pure iron, such as may be obtained by electrolysis. Unlike pure iron, too, steel presents a granular instead of a fibrous structure when broken; the best samples closely resembling silver in this respect. The chemical difference between hard and soft steel appears to consist in the much more intimate combination of the carbon with the iron in the hard variety than in the soft. In this latter kind the carbon seems to be only mechanically mixed, for if it be immersed in hydrochloric acid the iron is dissolved, and leaves the carbon behind. Steel is the most tenacious of all the metals, being greater than that of either cast or malleable iron.

What is termed _case-hardening_ (which _see_) is a process by which small articles of iron, such as keys, gun-locks, &c., are superficially converted into steel. It is performed by heating the articles in contact with iron filings or powdered charcoal. Another method is to make the iron substance red hot, and then to sprinkle powdered pota.s.sic ferrocyanide all over it.

=STEREOCHROMY.= This is a branch of the pictorial art confined to the embellishment of walls and monuments. In the operations by which it is accomplished it will be seen that the soluble silicates (water gla.s.s) play an important part.

The foundation for the future picture or coloured design must be of some durable stone or imperishable cement. Over this is first placed a layer of lime mortar, to which is applied when it is dry and has become sufficiently hard, a solution of water gla.s.s, by which all the interstices of the mortar are filled up. Another coating of mortar made of sharp sand and a lye of chalk is next laid on, and this, after it has been carefully smoothed, properly levelled on the surface, and become quite dry, is washed over and thoroughly impregnated with water-gla.s.s solution. When this last layer has become dry it is ready to receive the painting, which must be executed in water colours. After laying on these colours may be permanently fixed by covering them with water gla.s.s. The following are the colours used:--Zinc white, chrome green, chrome oxide, cobalt green, chrome red, zinc yellow, oxide of iron, sulphide of cadmium, ultramarine, ochre, &c. Vermillion is inadmissible, since, in fixing, it turns from red to brown. Cobalt ultramarine, on the contrary, increases greatly in brilliancy upon the application of the fixing solution. Stereochromatic paintings are found to be very durable, and impervious to damp, smoke, or variations of temperature.

=STE'REOTYPE METAL.= See TYPE METAL.

=STER'LING.= The truth of the old proverb, that "all is not gold which glitters," is often painfully experienced by the purchaser of modern jewelry. The following table will, therefore, prove highly useful to the reader in determining the value of articles in gold, provided he ascertain the 'fineness' of the metal, either by examination or written warranty:--

_Sterling value of Gold of different degrees of 'Fineness,'_

Carats. Value per Fine. oz. Troy.

_s._ _d._ 24 _carats_ 4 4 11-1/2 23 " 4 1 5 22 " (_British standard_) 3 17 10-1/2 21 " 3 14 4 20 " 3 10 9-1/2 19 " 3 7 3 18 " (_lowest Hall-mark_) 3 3 8-1/2 17 " 3 0 2 16 " 2 16 7-1/2 15 " 2 13 1 14 " 2 9 6-1/2 13 " 2 6 0 12 " 2 2 5-1/2 11 " 1 18 11 10 " 1 15 4-1/2 9 " 1 11 10 8 " 1 8 3-1/2 7 " 1 4 9 6 " 1 1 2-1/2 5 " 0 17 8 4 " 0 14 2 3 " 0 10 7-1/2 2 " 0 7 1 1 " 0 3 6

=STEREO-METAL.= A remarkable alloy recently invented by Baron de Rosthorn, of Vienna, and used in place of ordinary gun-metal. It consists of copper and spelter, with small proportions of iron and tin, and to these latter its peculiar hardness, tensile strength, and elasticity, are attributed.

=STETH'OSCOPE.= An instrument employed in auscultation. It consists of a tube (usually made of wood, sometimes of gutta percha) widening considerably at one end, and but slightly at the other. The wide end is applied to the chest or other part of the patient, the physician putting his ear at the other end; and from the sounds emitted by the heart, lungs, &c., the state of these parts is ascertained.

=STEW'ING.= A method of cooking food intermediate to frying and boiling, performed by simmering it in a saucepan or stewpan, with merely sufficient water to prevent burning, and to effect the object in view; the whole being served up to form the 'dish.' It is undoubtedly the most simple and economical, and, when skilfully conducted, one of those best calculated to develop the flavour and nutritious qualities of animal food. The following is one of the most popular stews:--

=Stew, Irish.= _Prep._ (Soyer.) Take about 2 lbs. of scrag or neck of mutton; divide it into ten or twelve pieces, and lay them in the pan; add 8 large potatoes and 4 onions cut into slices, season with 1-1/2 teaspoonful of pepper, and 3 do. of salt; cover all with water, put it into a slow oven, or on a stove, for two hours, then stir it all up well, and serve it up in deep dishes. If a little more water is added at the commencement, you can take out, when half done, a nice cup of broth.

=STILL.= A vessel or apparatus employed for the distillation of liquids on the large scale. The forms of stills, and the materials of which they are made, vary according to the purposes for which they are intended, some being exceedingly simple, whilst others are equally elaborate and complicated. The _engr._ represents the most common and useful apparatus of this kind, and the one almost exclusively employed in the laboratory.

It is used as follows:--After the fluid and other matters (if any) are put into the still, the head is placed on and connected with the worm-tub or refrigerator, and the joints are all securely luted. For ordinary liquids, a stiff paste made with linseed meal and water, to which a little chalk may be added, answers well for this purpose. For corrosive liquids, nothing is better than elastic bands or rings interposed between the joints, which are then 'brought home,' as it is called, with screws or clamps. Heat is next applied, and the worm-tub is supplied with cold water in sufficient quant.i.ty to preserve its contents at a proper temperature; the application of the heat being so regulated that the liquid may drop from the end of the refrigerator quite cold and unaccompanied with vapour.

For highly volatile liquids a closed receiver should be provided.

[Ill.u.s.tration:

_a._ Body of still, which may be either placed in a steam jacket or in a brick furnace.

_b._ Still head or capital.

_c._ Worm-tub.

_d._ Pewter-worm or refrigerator.

_e._ Cold-water pipe.

_f._ Waste-pipe.

_g._ Receiver.]

Of the various forms of distillatory apparatus that patented by Coffey in 1832 is the one almost universally employed in this country. It yields the strongest spirits obtainable on a large scale. Coffey's still (of which a drawing is given on the next page) effects a great economy in the expenditure of heat, by causing the liquid to be exposed to a very extended heated service; whilst it effects the evaporation of the alcohol from the wash by pa.s.sing a current of steam through it.

[Ill.u.s.tration: Coffey's Still.]

The wash is pumped from the 'wash charger' into the worm-tub, which pa.s.ses from top to bottom of the rectifier. In circulating through this tube it experiences a slight elevation of temperature. Arrived at the last convolution of the tube in the rectifier, the wash pa.s.ses by the tube M in at the top of the 'a.n.a.lyser.' It falls, and collects on the top shelf till this overflows, whence it falls on the second shelf, and so on to the bottom. All the time this operation is going on steam is pa.s.sed up from the steam boiler through fine holes in the shelves, and through valves opening upwards. As the wash gradually descends in the a.n.a.lyser it becomes rapidly weaker in alcohol, partly from condensation of steam which is pa.s.sed into it, and partly from loss of alcohol, either evaporated or expelled by the steam, till when it arrives at the bottom it has parted with the last traces of spirits.

At the same time the vapour, as it rises through each shelf of the a.n.a.lyser, becomes constantly richer in alcohol, and contains less and less water because of its condensation; it then pa.s.ses from the top of the a.n.a.lyser in at the bottom of the lower compartment of the rectifier. Here it ascends in a similar way, bubbling through the descending wash, until it arrives at F, above which it merely circulates round the earlier windings of the wash pipe; the low temperature of which condenses the spirits; which, collecting on the shelf at F, flows off by the tube into the finished spirit condenser.

To still further effect a saving of heat, the water for supplying the boiler is made to pa.s.s through a long coil of pipe, immersed in boiling spent wash, by which means its temperature is raised before it enters the boiler.

Another variety of distillatory apparatus is that of Siemens' (see page 1566), much employed in the distillation of brandy.

It consists of two mash stills set in a boiler, and capable of being alternately used by means of the three c.o.c.ks (_a_, _b_, and _c_). L is the boiler; P one of the mash retorts; K is the low wine receiver; R the fore warmer, a reservoir in which the condensed water intended as feed water of the boiler is collected; C is the dephlegmator; B a reservoir for the vapours condensed in C.

From the dephlegmator the vapour pa.s.ses to a condenser, not shown in the engraving.

The mash warmer consists of a cylindrical portion (_i i_), the lower part of which has an indentation (_c_). In the cylinder is placed a narrower portion (_o o_) of the real mash, containing a vessel, fitted with the heading tube (_f n_). The upper part of the fore warmer is fitted to the lower part by means of the f.l.a.n.g.e (_h h_); _r_ is a stirring apparatus, which is frequently set in operation during the process of distillation.

The vapours from the second still are carried into the depression (_c_) under the fore warmer, which, in order that the vapours may come into contact with the phlegma, is covered with a sieve.

[Ill.u.s.tration: Siemens' Distillatory Apparatus.]

The vapours surround the under part of the mash reservoir, and enter into the tube (_f_), through which they pa.s.s to the lower cylinder of the dephlegmator. The condensed water of the dephlegmator is conducted into the reservoir (A). The upper and under part of the fore warmer are made of cast iron, but the interior bottom and heating surfaces are made of copper. This kind of fore warmer has the advantage of uniformly distributing the heat, while it can be easily cleansed.

The dephlegmator (C) is so contrived that the rectified vapour can be conveyed to the condenser by two separate pipes placed in an opposite direction to each other, which are joined again in close proximity to the condenser.

The remainder of the details will be seen by studying the engraving.

Another distilling apparatus is that known as Derosne's, which is an improvement upon one invented by Cellier-Blumenthal. This apparatus is only designed for the distillation of wine, and not, like the previous ones, of mash.

The engraving on page 1568 gives a representation of it.

It consists of two stills (A and A'); the first rectifier (B); the second rectificator (C); the wine warmer and dephlegmator (D); the condenser (F); the regulator (E); a contrivance for regulating the flow of the fluid wine from the cistern (G).

The still A', which, as well as the still A, is filled with wine, acts as a steam boiler. The low wine vapours evolved come, when they have arrived in the rectifiers, in contact with an uninterrupted stream of wine, whereby dephlegmation is effected; the vapour, thus enriched in alcohol, becomes stronger in the vessel (D), and thus arrives at the cooling apparatus (F). In order that a real rectification should take place in the rectificators the stream of wine should be heated to a certain temperature, which is imparted to it by the heating of the condensed water. The steam from the still A' is carried by means of the pipe (Z) to the bottom of the still A.

Both stills are heated by the fire of the same furnace. By means of the tube B' the liquid contained in the still A can be run into the still A'.

The first rectificator (B) containing a number of semicircular discs of unequal size, placed one above the other, and which are so fastened to a vertical centre rod that they can be easily removed and cleansed. The larger discs, perforated in the manner of sieves, are placed with their concave surfaces upwards.

[Ill.u.s.tration: Derosne's Distillatory Apparatus.]

In consequence of this arrangement the vapours ascending from the stills meet with large surfaces moistened with wine, which, moreover, trickles downward in the manner of a cascade from the discs, and comes, therefore, into very intimate contact with the vapours. The second rectificator (C) is fitted with six compartments; in the centre of each of the part.i.tion walls (iron or copper plates) a hole is cut, and over this hole, by means of a vertical bar, is fastened an inverted cup, which nearly reaches to the bottom of the compartment wherein it is placed. As a portion of the vapours are condensed in these compartments, the vapours are necessarily forced through a layer of low wine, and have to overcome a pressure of a column of liquid two centimetres high. The fore warmer and dephlegmator (D) is a horizontal cylinder made of copper fitted with a worm, the convolutions of which are placed vertically. The tube (M) communicates with this worm, the other end of which pa.s.ses to O. A phlegma collects in the convolutions of this tube, which is richer in alcohol in the formost windings, and weaker in those more remote; this fluid, collecting in the lower part of the spirals, may be drawn off by means of small tubes, thence to be transferred, at the operator's pleasure, either all or in part, by the aid of another tube and stopc.o.c.ks, to the tube (O), or into the rectificator.

By means of the tube (L) the previously warmed wine of the dephlegmator can be run into the rectificator. The condensor (F) is a cylindrical vessel closed on all sides, and containing a worm communicating with the tube (O).