THE MANUGRAPH OR CHROMOGRAPH.

Akaroa Mail and Banks Peninsula Advertiser, Volume 4, Issue 385, 13 April 1880, Page 2

THE MANUGRAPH OR CHROMOGRAPH.

The nature of the chromographic or polygraphia pads, of which so many have of late heen sold in Cliristchnrch, is interestingly described hy Mr R. H. Ridout in Nature. He says :—A very elegani process has recently been introduced into thia country for copying and multiplying letters and documents. It is known by various names, according to the etymological skill of-the makers. One calls it a " hektograph," another less pardonably calls it the " centograph," while yet another, to bridge the gap between ancient Greek and modern English, styles it the " printograph." But whether it ie introduced by these names, or the polygraph, the compolithograph, or the velocograph, the principle is the same, though the details are slightly varied in each case. A slab of gelatinous matter in a shallow tin tray forms the type. The letter is written with a special ink on any kind of; paper, and when dry is placed face downwards upon the jelly, and allowed to remain a minute or more. On removal it is found that the greater part of the ink has been left behind on the jelly. It is only necessary to place pieces of paper on the latter, and on their removal they are found to be perfect facsimiles of the original copy. The number of copies obtainable varies with the ink, the most potent being aniline violet, such as Poirrer's. With this a hundred copies may be produced. Others, such Aβ bleu de Lyon, Bismarck brown or Roseine, yield 40 to 50. It was with a view to determine the principles which govern this beautiful process, that I made an examination of the subject. The Rlab consists of gelatine and glycerine, with carbolic or salicylic acid to prevent fungoid growth, an in the " chromograph " a quantity of barium sulphate is added, which gives the slab a white enamel-like appearance. « If a hot, strong solution of gelatine in water be prepared, and then a certain quantity of glycerine stirred in, the whole mass will become solid in cooling. This might at first sight appear to be a solution of gelatine in water and glycerine; but such is not the case, the gelatine being quite insoluble in glycerine. When the aqueous solution solidifies, the gelatine still retains the water, but the large quantity of glycerine being dispersed through the mass makes the whole into what is practically a fine gelatine sponge containing glycerine in its pores. The moisture-loving nature of the glycerine prevents the " sponge" from getting dry, while tlie insolubility of the gelatine in the glycerine prevents its becoming liquid. When the copy is placed on the jelly, the glycerine coined out to meet the ink, for which it has an intense liking. All the suitable inks .are freely' soluble in glycerine. Some, too, contain acetic acid either in the free state or in combination with liases, as in ro-anlline acetate. Tim acetic acid exerts a solvent action on the gelatine, so that it will bo found that after taking off some impressions with an acetic acid ink, as the "multiplex," the jelly will bo etched wherever the ink has come into contact with it. As long aa any ink remains on the jelly the glycerine will come out of .the pores to keep it moist, but when the whole of the ink has been removed the flow of glycerine ceases, and the parts become quite dry. If the ink is not entirely removed by tnking.a sufficient number of impressions, and the jelly left, after a lapse of twenty-four hours the remaining ink will be absorbed by the jelly. It is necessary, therefore, that the copies should be taken oft" as soon as possible, so as to avoid the defect caused by the spreading of the ink. , Most of the makers suggest that directly the slab is done with the type should be washed off. The hektograph and most others require that the water should be warm, but the finely divided barium sulphate in the chromograph renders the surface less tenacious, and the impression may be removed with cold water. Where practicable, it is better in all cases to leave the slab for twenly-four hours, when the old impression will be quite absorbed, and not interfere with a newone. 1 his gelatine"copying process has been received with so much favor by the public that it shows there is a great went ;for some rapid means of getting a limited number of copies of letters, &c ; and seeing that any number of colours may be used in the original drawing, Mr Norman Lockyer has suggested that it would b« of much use in laboratories for the multiplication of original sketches of biological specimens, and even for spectra charts, and so save much of the time spent in making duplicate copies- The gelatine slab cannot be said to be perfect, as it is liable to be affected by atmospheric changes; but, bearing in mind the fact that the whole is simply a sponge filled with a compound capable of liquefying certain inks, it is reasonable to hope and expect that chroniography is only the pioneer of a proces3 which shall possess all its advantages and none of its defects.