M. TECHNOLOGY. 605 



ing, for fixing it thoroughly ; and it may, indeed, be printed 

 at the same time with most of the other colors, such as aniline 

 blacks, etc. Its preparation consists in thickening with gum, 

 or other thickener, a sufficiently concentrated solution of 

 white indigo in an alkali or alkaline body, and then adding 

 to the mixture the proper quantity of hydrosulphite of soda. 



TO COLOR CHAMOIS OX HALF-AVOOL GARMENTS. 



For ten pounds of material prepare, in a perfectly clean 

 kettle, with soft water, a bath of about one fourth of a pound 

 of annatto ; heat, add the garments, heat to boiling, and boil 

 for half an hour ; then rinse well, pass through a w^eak warm 

 sulphuric acid bath, and again rinse well. 26 C\ 1873, 167. 



IMPROVED GUM-ARABIC MUCILAGE. 



A serious objection to the use of gum-arabic, as an adhe- 

 sive, is found in its showing through unsized paper, and thus 

 producing a semi-transparent blot. This is also attended 

 with the still greater inconvenience that the two layers do 

 not stick together satisfactorily. On this account gum-ara- 

 bic mucilage can not be used for attaching paper to paste- 

 board, nor wood to wood, nor one metallic substance to an- 

 other, since the gum soon peels offi All this inconvenience 

 may be remedied, it is said, by adding to the gum a solution 

 of sulphate of alumina; two parts of crystallized sulphate of 

 alumina answering for one hundred and twenty-five parts of 

 the concentrated solution of gum-arabic, in the proportion of 

 two parts of gum to five of water. The salt is to be dissolved 

 in ten times its weight of water, and the solution mixed di- 

 rect with that of the gum solution, w^hich in this condition 

 well deserves its name of vegetable glue. A solution of 

 alum replaces the sulphate of alumina, but to a much less 

 satisfactory degree. 18 C\ July 2, 1873, 428. 



CEMENT FOR FASTENING METALS ON GLASS. 



The following cement, recommended by Franke, for fasten- 

 ing prize-medals, electrotypes of badges of honor, etc., upon 

 the show-cases in the Vienna Exposition, instead of the tedi- 

 ous and defective method of boring the glass^with its liabil- 

 ity to fracture, may be found generally useful in fastening 

 metal on glass securely and rapidly. To an intimate mixture 



