302 



THE CIVIL ENGINEER AND ARCHITECT'S JOURNAL, 



[OCTOBEB, 



colour nsed l)cinff suitaWe fur the colour of the groiind of the paper. 

 The paper so treated having been properly dried, is laid on a board 

 with the coloured surface uppermost, and the workman ]>roceeds 

 to g-ive it a coating of the matter known in the trade as " satin 

 white," or it may be satin white mixed with a colour; this isapi>lied 

 to the whole surface of the paper, by means of brushes; he tlien 

 ])roreeds to delineate the marl)le on the moist or wet siirface of the 

 pajier, produced by the ajiplication of the satin white, and, by 

 preference, putting on what is called the veining first, which is 

 ])erformed with the ordin;iry crayons, the colours of which are 

 suitable to ]iroduce the veining required for the diaracter of the 

 marble. The veining is ne.xt softened off by the ordinary softening 

 brush, in order to blend the colour of the veining slightly with the 

 groundwork or coating of satin white, so as to break the harsh- 

 ness of the outline; the colours are then applied, while the satin 

 white is still in a moist or damp state, introducing them with 

 brushes, in imitation of the kind of marble or porphyry to be re- 

 ]>resented; these colours are then smoothed down, or subdued and 

 blended with tlie ground or coating of satin white. Thus it will 

 be seen, the whole of the colours, with the exception of the pre- 

 paratory coating mentioned, are introduced while the satin wiiite 

 is still wet, after which it will be complete, as far as regards the 

 effect to be produced by the colouring matter, when it may be 

 dried in the ordinary manner. The colouring matters used are 

 the same as those employed in ordinary in the production of 

 marble papers; hut instead of being prepared simply as water 

 Colours, used in the ordinary manufacture of hand marble papers, 

 they are prepared with a proportion of satin white, that the colour 

 shall also present a surface capable of receiving the polish or gloss 

 to be imparted to it. 



In manufacturing granite papers according to this invention, 

 tlie patentee also employs paper previously prepared with a coat- 

 ing of colour, as a groundwork, which, while in a dry state, 

 receives a coating of satin white, coloured or otherwise, it being 

 laid out on a board, as before described with reference to mai'ble 

 l)aper, while this coating of satin white is yet in a moist or damp 

 state; the colouring matter is then applied in imitation of granite, 

 by s|)lashing or otherwise causing the colour to adhere in spots to 

 the satin white. Tliis operation being common in tlie manufacture 

 of granite papers, further description of the process will be un- 

 necessary. 



The colours used in splashing in imitation of granite are also 

 prepared with a proportion of satin white, in order to render tlie 

 colours of tlie constituent proportions necessary to produce the 

 de.sired effect, by rubbing or polishing. It is not necessary that 

 tlie colour used as the preparatory coating should contain any 

 satin white, either for the marble or granite papers. Marble and 

 granite papers, when prepared in this manner, after having been 

 thoroughly dried, are then subjected to the process known as 

 "rubbing,' for the purpose of imparting the desired gloss or 

 polish; the machine known as a "rubbing machine" is employed 

 for this purpose, and which consists of a cylindrical brush, of a 

 sufficient length to operate upon the whole width of the paper. 

 This brush is caused to rotate rapidly, and during such rotation, 

 to bear against a surface or table, between which and the brush 

 the ]iaper is passed, having the marbled side of the paper next the 

 brush, which marbled surface is previously dusted or rubbed with 

 French chalk, in a state of powder, as a polishing material. The 

 end of the paper having been introduced between the brush and 

 the table, the rotary motion of the former draws in the paper 

 from the roll, which is supported so as to unroll freely, yet taking 

 c-'ire that a sufficient amount of friction is exerted on the paper as 

 it passes over the table, to prevent its too rapid jiassage under the 

 brusli. The paper, as delivered from the machine, is in a finished 

 state, presenting the glossed or polished appearance required on 

 the marble or granite surface. 



Enamels for Iron. — This invention, patented in America by Charles 

 Stumer, consists in providing an enamel for iron and other metals which 

 will retain its adhesion to the metal, and particularly it is not capable of 

 being crumbled or broken off by blows or by heat, this possessing the quality 

 of comparatively co-mingling with the surface of the metal. Thus it is far 

 superior to any known enamelling for metals, and may be modified so as to 

 render it in all the shades of colours, in full variety. — Composition A: 

 IG oz. of gravel sand, 10 oz. of silver glass (silver gilt or silver gilding), 

 2 oz. of white clay, |-oz. of saltpetre. — Composition B: 1 oz. of glass 

 (common white glass), 4 oz. of gravel sand, 8 oz. of zean reanocks (or oxide 

 of tin), 6 oz. of borax, 1{ oz. of soda, 3 oz. of saltpetre, Ij^-oz. of white- 

 clay, 1 oz. of magnesia, ^-oz. of white chalk, ^-oz. of oyster shells — this should 

 be pulverised, like Composition A., and then mixed with the gum water. 



TUB FLEXURE OF POSTS. 



lipmarks on the, Resi-itance of Posts to Fh.xure. By H. Iloupr, 

 C.E. — [From the American Journal of the Franklin lH>ititute.'\ 



The ordinary formula for the stiffness of beams, supported at 

 the ends and loaded in the middle, is 



UP 



in which (w) represents the weight which produces a given de- 

 llection; b r= breadth in inclies; d = depth in inches, and I = 

 length in feet; c is a constant, to be determined by substituting 

 the values of the other quantities in the equation. 



In making experiments to determine the constant from this 

 formula, it is necessary to observe very accurately both the 

 weights and the deflections produced by them, and then, by means 

 of a proportion, find the value of (w), which will produce the de- 

 flection required to be substituted in the formula. 



In reflecting upon the circumstances connected with the flexure 

 of beams, the writer conceived the idea of deducing an expression 

 for the weight which a post would support from the ordinary 

 formula for the stiffness of a horizontal beam, by the following 

 considerations: — If a beam is bent by an applied weight, there 

 will be a tendency, from the elasticity of the material, to recover 

 its form when the weight is removed; but if the ends are fastened 

 by being placed between resisting points, so that tlie piece cannot 

 recover its shape, there must be a horizontal force caused by the 

 reaction of the material, and this force is such, that if the beam 

 were placed in a vertical position and loaded with a weight equal 

 to it, the deflection should be the same as that of the horizontal 

 beam, and consequently the extreme limit of the resistance of the 

 post to flexure would be determined. 



To ascertain the force which is exerted by the reaction of a 

 bent beam in the direction of the chord of the arc. 



Let AB represent a beam, supported at the ends and loaded 

 with a weight (w) applied at the middle point. 

 d =: deflection caused by the applied weight. 



BC = tangent of curve at B. 



If the weight be removed, the reaction of the beam will cause 

 it to regain its original figure if not resisted by a pressure at the 

 ends. Tlie force of this reaction will be propoi-tional to the de- 

 gree to which the fibres are strained, and as the strain upon the 

 fibres is nothing at the ends A and B, and inci-eases uniformly to 

 the middle point, the force of reaction will be in the same propor- 

 tion, and the point of application of the resultant of the whole of 

 the reacting forces will correspond to the centre of gravity of a 

 triangle whose base is B/; it will consequently be at a distance 

 from B = I B/. 



The effect of this resultant acting at a distance g B/, must be 



the same as the weight ( ^^ I acting at a distance Tif, and must con- 



w 

 sequently be in proportion to — as 3 : 2. The value of the result- 



. , ,- 3 IV 

 ant is therefore — . 



4' 



The line of direction of the pressure at B being the tangent 

 BC, the force of reaction at It may be considered as applied at the 

 point k of its line of direction, and as k h B and Cy" B are similar 



triangles, C/:/B 

 5 "' 21/ ~ 16^' 



; f Ml : horizontal pressure at B : 



•? f^ 



^w %•'-—,= 



Vc 



B = 



Representing this force by P, we have 



3wl 

 i6~d' 



As the deflection of a beam within the elastic limits is always in 

 proportion to the weight, if («/) = the weight that will produce a 

 deflection equal to unity, the deflection (rf) will require a weight = 

 (rfu)'), and by substituting this value in the equation, we find 



