MECHANICS AND USEFUL ARTS. 97 



surface applied, after which it is allowed to dry. The sheet of mica 

 can be easily rendered adherent to almost any article by glueing. 

 Mr. Murray then takes a pattern of copper, with a design cut out on 

 it, and places it on the reverse side of the mica, and with a small 

 brush removes any superfluous parts, the required design thus re- 

 maining on the parts which have not been brushed. He then applies 

 colors, either one or more tunes, as considered necessary, and after- 

 wards coats the whole with a solution of liquid glue diluted in spirits 

 of wine, which is applied for the purpose of rendering the mica plia- 

 ble. When this is effected, the mica with the design upon it is ap- 

 plied to the frame of the other object and fastened with glue. In 

 order to make the junctions of several pieces of mica imperceptible, 

 Mr. M. first glues them together with Y enet i an glue, and then applies 

 a hot iron to the parts where the mica is joined together, when the 

 parts will be completely united. 



The value of mica depends upon the size of the sheets and their 

 transparency, the clear ruby-tinged being the finest, and the cloudy 

 gray the least valuable. The best mica in the English market is now- 

 imported from Calcutta and Siberia, and is at present readily salable 

 at from 60 cents to $1.00 per pound. 



CHROMO-TYPOGRAPHY. 



Although block books in colors are as old as printing in China, pic- 

 torial printing in oil-colors on the platten and cylinder press is a 

 thing of the present day. Such, however, has been the rapid devel- 

 opment of this art, that prints on which twelve colors are required 

 are now thrown off with the rapidity of newspapers on a steam-press. 

 The well-known colored prints which accompany the London Illus- 

 trated News are specimens of this style of chromo-typography ; and 

 so great is their beauty and popularity that of some favorite issues 

 two hundred and fifty thousand copies have been struck off 



ADHESIVE STRENGTH OF GLUE. 



At the International Exhibition, 1862, a manufacturer of glue 

 showed a wooden bar, having a sectional area of one square inch, 

 sawn across and united by glue. This joint resisted a tensile strain 

 of five hundred and four pounds. 



INGENIOUS PLAN OF CORRESPONDING IN CIPHER. 



The New York Evening Post states that the following mode of 

 corresponding in cipher has been devised and used during the pres- 

 ent civil war: Each correspondent is provided beforehand with a 

 page printed from the same form, which may be any connected arti- 

 cle in a book or paper, or merely the several letters of the alphabet 

 arranged in parallel lines with the more common letters repeated a 

 proper number of times. Then the correspondent who writes to his 

 friend lays his sheet over a sheet of white paper and punches out 

 the letters to spell his words, driving the punch through the sheet 

 below. The white sheet is then forwarded to the correspondent, who 

 lays it over his printed sheet, and spells out the words which are 

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