736 GRAUWACKE 



On this point M. Jaquelain narrates one of his own recent experiments. On do- 

 composing some sulphide of carbon in a porcelain tube in presence of pure copper, 

 heated to about 800, sulphide of copper and graphite were formed, the latter exter- 

 nally similar to natural graphite. Cosmos, 1864, pp. 720, 725. 



Some of the latest researches of Gustav Kose, published just before his death in 

 1873, were directed to the natural forms of carbon, including graphite. For those 

 the reader may be referred to the ' Proceedings of the Berlin Academy of Sciences.' 



GRAPHOTYPE. By this new process of engraving (discovered in the summer 

 of 1860 by Mr. De Witt Clinton Hitchcock) the artist becomes his own engraver, and 

 thus overcomes the difficulties met with in most other processes, arising from the 

 impossibility of two individuals working out the same idea in exactly the same way. 

 A short description of the circumstance which led to this discovery will give a good 

 idea of the nature of the new method called ' Graphotype.' Mr. Hitchcock was 

 engaged in making a drawing on boxwood, and finding it necessary to erase a portion 

 of his work and re-whiten his block, he took a visiting-card (the white material usod 

 for the surface of the wood engraver's block being of the same composition as the 

 enamel of the said card) and commenced rubbing off the enamel with the aid of a 

 brush and water, when, to his astonishment, he found the printed letters remained in 

 relief. The ink in combining with the enamel had become sufficiently hard to resist 

 the action of the brush, and thus he had accidentally prepared a sort of block upon 

 which the letters stood out. This circumstance led him to the discovery that by 

 taking a slab of chalk, reducing its surface to as smooth a condition as possible, draw- 

 ing on it with an ink composed of silicate of potash (water-glass) and indigo, then, 

 when the sketch was dry, by brushing away the surface with a dry brush (the lines 

 of the drawing being virtually converted into stone, they will withstand the friction 

 of the brush, while the intervening particles are easily removed), and saturating the 

 mass of chalk with liquid glass, he had a block ready for printing from in the ordi- 

 nary way of burnishing. 



This experiment was successful, and after several trials the following method has 

 been adopted as the most perfect : A chalk surface upon a metallic plate is now 

 adopted. French chalk is ground to the finest powder, then the coarser particles sepa- 

 rated from the finer by being thrown into water, the sediment which first subsides 

 is removed and ground again ; this is repeated several times. Next, the powder is 

 repeatedly passed through a wire cloth which contains 10,000 holes to the square inch, 

 and is then laid between a smooth metallic (zinc) plate and a smooth steel plate, and 

 submitted to intense hydraulic pressure, then, after the chalk-surface is sized, it is 

 ready for the artist. The pencils employed by the artist are of sable-hair, and the ink 

 is composed of lamp-black and glue. When the drawing is finished the surface 

 is gently rubbed with silk velvet, or fitch hair-brushes, until the chalk between the 

 inked lines is all removed to the depth of about the eighth of an inch. After this the 

 block has only to be hardened, which is done by soaking it into a solution of an 

 alkaline silicate (water glass) ; by this means the whole of the chalk is converted into 

 stone. 



This petrified block is not used to print with, as it would not stand the wear and tear 

 it would be subjected to in the printing press, but a mould is taken of it, from which 

 a type-metal cast (a stereotype) is made, and it is this stereotype from which the im- 

 pressions are taken. 



One of the great merits of this new process is the extreme delicacy and precision 

 with which the finest lines are produced, and the accuracy and rapidity of production 

 are the two great recommendations of the graphotype. A sketch made in the morning 

 may be multiplied by thousands by the evening. The graphotype is a most valuable 

 invention ; and it seems probable that it will supersede the old wood-engraving to a 

 considerable extent : it is cheaper, more accurate, and more rapid of production, but 

 still it possesses all the advantages of the ordinary block. 



GRASS-OXXi. A fragrant oil which is extracted from a peculiar Indian grass ; 

 it is generally called the grass oil of ftemaur. Grass-oil, on account of its odour, is 

 often termed lemon-grass or verbena ; it is derived from the Andropogon Nardus, a 

 species of grass which is now regularly cultivated in Ceylon for the sake of the essen- 

 tial oil which it yields by distillation, about 10,000 Ibs. of which are imported 

 annually. A. citratum has been considered to be the source of the oil of lemon- 

 grass. 



GRATE, a mining term. A metal plate pierced with small holes : it is fixed in 

 front of the stamps in which the ore is pounded, and through the holes the finely- 

 divided matter makes its escape. 



GRATTWACXE or GREYWACXE. (Grau, grey; wacke, clay.) A German 

 name, often adopted by geologists for some of the most ancient fossiliferous strata. 

 The rock is often of a grey colour, hence grew, German for grey ; wacki being a pro- 



