TO ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



CHROME ALUM. 



Much has been said, of late, of a substance known as 

 chrome alum, which has been used in the Albert and Edward 

 process of electrotype printing, for the purpose of hardening 

 the gelatine film and rendering it insoluble in water. In- 

 quiries have been pressed in various quarters for the recipe 

 lor preparing this substance, and we find in the Mechanics' 

 Magazine a reply, in which it is stated that if three ounces 

 of bichromate of potash be dissolved in as little boiling water 

 as possible, and then four ounces of strong sulphuric acid be 

 added, and afterward alcohol, drop by drop, be introduced, a 

 pure green tint will be developed. The liquid should be 

 stirred frequently during this process, and then boiled down 

 to a small volume and set aside. After a few days violet 

 crystals separate, which, when washed with pure water, are 

 said to be sufficiently pure for ordinary purposes. 18 A, 

 May 12,190. 



IMPROVED TEST-PAPER. 



A new test-paper of extreme sensitiveness can be prepared, 

 it is said, from the leaves of the ornamental plant known as 

 the Coleus verschaffelti. The fresh leaves of the plant are to 

 be steeped for twenty-four hours in absolute alcohol, to which 

 some drops of sulphuric acid have been added, and the liquid 

 afterward filtered. Into this are to be dipped strips of Swed- 

 ish filtering-paper, which are then allowed to dry in the air. 

 A test-paper of a beautiful red color will thus be obtained, 

 which will pass more or less into a fine shade of green by the 

 action of alkalies or alkaline earths. This paper will keep 

 for a long time if preserved in well-closed jars, and will be 

 found much more sensitive than the ordinary tests. It is not 

 affected by carbonic acids, but indicates the least trace of the 

 carbonates or alkaline earths that may be dissolved in water. 

 If a band of this paper, slightly moistened, be exposed to an 

 open gas jet, it will change rapidly to green, in consequence 

 of the ammonia contained in the gas. 2 B,May 14,539. 



ACTION OF WATER-GLASS. 



In a communication by Fluckiger upon certain reactions of 

 water-glass, some important technical applications are sug- 



