M A JS UFACTURES.

819

auufac- round and polished, the latter effect being produced byv — U ^ C — , Ihe hole being rather smaller than the pencil, wherebyp . the wood is compressed and polished, as above stated.P*nei? S for (1140.) Cutting leads for pencil cases, —The piecescases. °f lead for the pencil cases, the original Patent of Mr.

* Mordan, are cut from slices of plumbago, such as is de-

scribed above, first into square prisms of proper dimen-sions for forming the cylindrical pieces, which are thenmade round by forcing them lengthwise through threedifferent sized circular holes cut in pieces of ruby. Inpassing through the first hole only the four angles of theprism are taken off ; it is then of course octagonal; thenext hole, which is smaller, takes off these eight angles,and it then becomes a prism of sixteen sides, and in thenext passage through the smaller hole it attains the truecylindrical figure.

The manner of forcing the lead through the severalholes is not much unlike that in which the lead is forcedup in the pencil case itself; that is, in a piece of metalabout three inches long is a hole lengthwise, just bigenough to receive the first prism, and at the other endof this is the ruby hole mentioned above. This pieceof metal runs in a groove to preserve its direction, andthe end of a steel pin, fixed in an upright piece of iron atthe proper height, is introduced into the hole into whichthe lead is dropped, and a boy then presses the movablepiece of metal containing the lead against the pin, whichforces the piece forward through the ruby hole cuttingoff its angle as above described. A number being thuscut, he passes them all in the same way through thenext, and lastly through the third hole, when they areready for use.

Glue.

Grl

(1141.) This is a substance used in various processes,as in making size, but more especially by joiners, carpen-ters, and other artisans; the consumption of which there-fore is considerable, and some rather large establishmentsar e appropriated to its manufacture. The English isreckoned the best, and is exported to other Countries.This substance is made of the skins of all kinds of beasts,oxen, calves, sheep, &c., or rather from fragments of them,ns whole skins are too valuable to be thus employed exceptin very rare cases, that is, for glue of the best quality.

The materials above enumerated are first digested,n lime water to cleanse them from grease or dirt; theynre then steeped in clean water with frequent stirring,nnd afterwards laid in a heap and the water pressedA °ut; they are then boiled in a large brass caldron with

o'ean water, skimming off the dirt as it rises, and it isurther cleansed by putting in, after the whole is dis-T?i, Ve ^’ a NMc melted alum or lime finely powdered,th 6 skimmi »S i- s continued for some time, after whiche mass is strained through baskets and suffered toe le, that the remaining impurities may subside; it isev en P 0l,re< l gradually into the kettle again, and further®P°rnted by boiling and skimming till it becomes ofd be T < ark brownish colour. When it is thought to

nbcnit 01 "^ enou Sb> it is poured into frames or mouldsgradu Tl* ' on =’ one broad, and two deep, where itby * y hardens as it cools, and is cut out when coldin a sort 6 f ' nt0 sc i' lare cakes. Each of these is placed’ back • ii Wo °den box, open in three divisions to the

three slic 1 ■ the S ,ue > while it is still soft, is cut into

i place of h? a k ' nt ^ bow, with a brass wire in the

e string; now the slices are taken into the

•«*

open air and dried on a kind of coarse network, fastened Mechanic;,in movable sheds four feet square, which are placed in Processes,rows in the glue-maker’s field ; having become perfectlydry and hard it is fit for sale. The best glue is thatwhich swells considerably without melting by three orfour days’ immersion in cold water, and recovers itsformer dimensions and properties by drying. If theglue should be injured by frost, or look black and thick,it is necessary to melt it over again. The purchasermay easily detect bad glue by holding it before thelight, for if good it will appear of a strong dark colourand free from cloudy and black spots. Carpenters com-monly break the glue in small pieces and soak it four andtwenty hours in cold water, and then melt the pieces,allow it to simmer very slowly over a fire, and keepingit frequently stirred ; when done in this way it becomes,when cold, a firm jelly, which may be cut by any instru-ment. It only requires to be warmed to be fit for use,and in this state spread over the surface of the woodwith a stiff brush; in two or three days the pieces ofwood will be so perfectly cemented that boards thusjoined will as readily break in any other part as at thejunction. Glued boards will not set in a freezing tem-perature, the stiffening being occasioned by the evapora-tion of the superfluous matter of the glue, which is pre-vented by a considerable degree of cold.

The above is the usual kind of glue, and of which thelargest quantities are employed; but there are otherkinds of glue used for particular purposes which it willbe proper to speak of in this place. Of these, fish glueis the most important, which is made of the skins andmucilaginous parts of fish. These, being boiled, bear anear resemblance to that viscid matter found on theskin of cod-fish. When boiled to the consistence of ajelly it is spread on a leaf of paper and formed intocakes, in which state it is fit for use. Fish glue is muchused in medicine and many other Arts; hut this isbetter known under the name of isinglass and ichthyo-colla. A strong glue may be prepared with isinglassand spirits of wine, by steeping the isinglass for twenty-four hours in spirits of wine or common brandy. Whenthe menstruum has opened and mollified the isinglass,they must be gently boiled together and kept stirringtill they appear well mixed, and until a drop of it allowedto cool will soon turn to a strong jelly; it is now to bestrained through a clean linen cloth into a vessel to bekept close stopped. A gentle heat suffices to dissolvethis glue into a transparent and almost colourless fluid,but very strong, so that pieces of wood glued togetherwith it will separate as easily any where as in the partsjoined.

A strong compound glue may be made by infusing amixture of common glue, in small pieces, with isinglassglue, in as much spirits of wine as will cover them, forabout twenty-four hours; then melt the whole together,and as much powdered chalk is to be added as willmake it an opaque white. By dissolving gum sandaracand mastic, of each two ounces, in a pint of spirits ofwine, a strong glue may be obtained which will resistmoisture; an ounce of clear turpentine must be addedto the above mixture, equal parts of isinglass and parch-ment glue, pounded into small pieces ; the solution of thegum is to be poured upon them, and the mixture meltedin a covered vessel with a heat less than that of boilingwater, then the glue, after being strained through acoarse linen cloth, is to be again placed over the°fire,and an ounce more of powdered isinglass added to it.