GIN. 



GIRDERS. 



3-4 



(or more properly the chloride) of gold with sulphuric ether or alcohol. 

 By combining these liquid* together, an alcoholic solution of gold is 

 formed, from which the meUl U precipitated by the iron or uteeL 

 Hany applicatiooi of gilt metal are now superseded by the remark- 

 able electrotype process in the way described in the article already 

 adverted to. 



Wood-' Hiding. Wood work, whether plain or carved, is gilt l>y 

 the following processes. Parchmcnt-sizo is dissolved in water by 

 heat, and a httie whiting mixed with it. This composition is 

 brushed over the picture-frame or other article to be gilt. The 

 hole* and cracks that may be in it are then filled up with a mixture 

 of the same ingredients in different proportions, and of about the con- 

 litttmm of putty. A composition of the same sort, but containing 

 more whiting than the first, U then brushed over it, and allowed to 

 dry. This is repeated several times, till a considerable thickness has 

 been laid on. The plain parts are then moistened, smoothed down 

 with pumice stone and water, hard stone and water, Dutch rush, 

 glass paper, and other substances ; and the corners and mouldings are 

 squared and shaped by proper tools. When dry the work is covered 

 with several coatings of gold-size, a peculiar composition, of which 

 deer's fat U said to form the principal ingredient. The frame or other 

 article thus prepared, is placed in a sloping position; its parts are 

 successively moistened with water; gold-leaf is laid on them by a 

 " tip " (a sort of comb formed by inserting a row of camels' hairs into 

 a card), and U pressed down into the cavities by a dry camel's hair 

 pencil. The gold when dry U burnished by a stone in some parts ; 

 while others are left mat or dead, and are protected by a varniah of 

 very clear size. 



This constitutes luntiA-yildtag. Oil gilding differs from it chiefly 

 in the use of a gold-size of an oily nature, which admit* of no burnish- 

 ing of the gold. Jnpan-yitdimj is a third kind, in which Japan gold- 

 size is used, for work intended to be exposed to the weather. 



The applications of gold-leaf to leather, paper, wood, and other 

 Hubstauces, are numerous and diversified ; but what has been said above 

 will be sufficient to indicate the principles and details of this branch of 

 the arts. It may be well to add, that glass may be gilt by the following 

 simple method : Dissolve some isinglass in water by means of heat ; 

 evaporate the liquid, and allow it to crystallise. Re-dissolve gome of 

 the crybtala, and after making the mixture of the usual consistence of 

 glue, dip into it a piece of clean chamois leather, which is to be drawn 

 once, and only once, over the parts of the glass that are to be gilt. 

 Lay on the leaf-gold, which will adhere, and allow the whole to dry. 

 On this coating of gold another may be placed in a similar manner, 

 being careful to draw the isinglass only once and lightly over the 

 former coating. It will be generally found advisable to repeat this 

 process a third time. Any superfluous gold may be removed by a 

 sharp stick, and the gilt parts are to be polished by rubbing them with 

 clean cotton, which will obliterate all traces of any joinings, and 

 prevent them from being visible from either side of the glass. 

 GIN. [CuTTox ; GENEVA.] 



GIN, or GYN, a machine employed instead of a crane, chiefly by 

 artillerymen, for the purpose of raising guns, howitzers, Ac., on their 

 carriages. It consists of three round poles, from 12 to 15 feet long, 

 and 5 inches in diameter at the lower extremity, tapering to about 

 3( inches at the top. 



The three poles are, by means of an iron bolt passing through straps, 

 or by a rope passed several times round each, united together at their 

 upper extremities in such a manner that they may be turned about 

 their place of union ; and when the machine is set up, the feet of the 

 pole* are planted in the ground at about 8 or 9 feet from each other. 

 The feet of two of the poles are kept at that distance by means of a 

 rope or an iron bar, which may be temporarily placed in a horizontal 

 position near their lower ends ; and between the same two poles, at 

 about 84 feet from the ground, is a wooden roller, or windlass, which, 

 by means of handspikes, may be turned on its axis, the pivots entering 

 into holes sunk in iron cheeks attached to the poles. The third 

 pole, commonly called a " pry-pole," has a greater extent of movement 

 than the others about the upper extremity, so that all the throe poles, 

 previously to being set up, may lie on the ground. The gyn is then 

 set up over the object to be moved ; two blocks with their fall, or 

 rope, are employed in raising or lowering the gun, the upper block 

 being fixed to the top of the poles, and the other, by means of a rope, 

 to the piece of ordnance : the rope from the upper block passes over 

 the windlass before mentioned. 



Two poles fastened together at the top, and set up like the side* oi 

 the letter A, the whole being kept steady by means of ropes made fast 

 to the upper extremity and to strong pickets driven into the ground, 

 are also employed for raising or lowering artillery, by means of two 

 blocks with their rope, the extremity of the latter usually passing round 

 the cylinder of a windlass, capstan, or crab. This apparatus is colled 

 shears. 



GIPSIES. [GYPSIES.] 



OIRDEKS. The timber or Iron beams, employed in building 



operations to carry loads over large openings, are known technically by 



the name of (-irdert, either simple or framed. The former will alone 



be noticed here. 



A simple girder resist* the action of the weight brought upon it by 

 it* inherent transverse strength, and it must be evident to any one 



who would observe the manner of fracture of any such beam, that the 

 fracture is produced by the extension of the lower fibres, and by the 

 compression of the upper ones, whilst the intermediate part of the 

 beam plays but an insignificant part in it* resistance, so long as 

 the upper and the lower portions are not overstrained. Theoretically, 

 then, the middle parts of a beam might almost be eliminated, because 

 they not only do not render any service, but they actually tend to 

 increase the load by their weight ; but, from the physical nature of 

 the materials usually employed as girders, it is hardly possible to 

 attain this condition, and the efforts of the constructors are therefore 

 limited to the attempt to approach, as nearly as may be, to the form 

 of a girder of the maximum resistance with the minimum quantity of 

 material. This form varies with every description of wood, or of 



n ; but the character of the growth of timber renders it unnecessary 

 to pay much attention to the varying resistances of it* fibres to com' 

 pression or extension ; whilst, on the contrary, it is easy to modify the 

 disposition of the metal, whether wrought or cast, so as to call into 

 play its various properties under the most economical conditions. 



The strength of a simple timber girder is found, experimentally, to 

 increase directly as the width, and as the square of the depth ; or, if 

 a beam of 6 inches on the sides bear a certain weight, two such beams 

 will bear twice that weight, and a beam of twice the depth will bear 

 four times the weight ; the strength is likewise inversely as the length. 



These ratios are usually expressed by the formula , in which I - 



the breadth, rf the depth, and I the length ; and it requires simply to 

 be modified by a coefficient, dependent upon the specific strength of 

 the kind of timber under consideration, to furnish a correct indication 

 of the powers of resistance of a girder ; or the breaking weight in 



pounds of a girder will be represented by , in which the new 



term, c, is the constant of the wood. Barlow, Nelson, Moore, and 

 Deunison give, in the papers of the Koyal Engineers, a table of con- 

 stants which is now generally adopted ; and from the fact that the 

 results it indicates are considerably within the real capabilities of the 

 various woods, there seems to be no reason for objecting to it : 



The manner in which a load is applied to a beam, it must however 

 be observed, considerably modifies its resistance ; for if the load be 

 distributed equally over the whole length, the beam would carry twice 

 as much as it would do if the load were concentrated in the centre. 

 Again, if the ends of the beam be fixed, the breaking weight it wouM 

 carry would be increased, upon the average, nearly in the ratio of 

 2 to 1. The values of r, given above, have been ascertained from the 

 results of experiment* on beam* whose ends were loose ; but as the 

 effect of a permanent load (in producing fracture) is so markedly 

 greater than that of an instantaneous load, it is not customary to take 

 into account the increase of resistance of girders through the tying 

 down of their ends, which in fact almost always occurs in building 

 operations. The values of the above table are the instantaneous 

 breaking weight* of the average qualities of the woods named, and 

 therefore the weight actually placed upon them should never exceed 

 one-third of the amount they indicate ; or, in other terms, the safety 

 load of a beam should never exceed one-third of the breaking weight. 

 liufTon states that he had found that beams would break at the 

 six months under two-thirds of the load they might be able to support 

 for one day. It is essential also to observe that the character of the 

 load will affect the resistance ; for a dead weight produces a far less 

 injurious action than would be produced by a rolling or a variable 

 weight ; and that the various kinds of wood yield in very different 

 manners. Some of them deflect in an extraordinary degree, whilst 

 others change but slightly in their outlines, and break suddenly, 

 without warning, after their limits of elasticity have been exceeded. 



The form of beams which is able to do the maximum amount of 

 work with the minimum amount of substance is usually considered to 

 be, according as the beam is supported at one or at both ends (W.irr'a 

 ' Dynamics,' 1851), as follows : For beams supported at one end ; 

 1. a. If the load be constant, and applied at the extremity, and the depth 

 of the beam be also constant, the transverse Motion should diminish 

 gradually from the point of support towards the extremity ; 6. If the 

 breadth be constant, the depth should vary as the length ; if both 



