216 ANNUAL OF SCIENTIFIC DI3COVEHY. 



parts of solution of copal, two parts of that of sandaraeh, and four parts of 

 toiu'iion of damara resin (equal parts of resin ami absolute alcohol), are mixed 

 with half their volume of oil of bergamot or rosemary. This mixture is to 

 be evaporated to the thickness of castor oil. If this varnish be then drawn 

 by the means of a feather or brush over the surface of some water, it will 

 form a beautifully irridescent pellicle. This film is now to be applied to the 

 objects which are to be rendered irridescent. The vessel in which the water 

 is contained, on- which the pellicle has been produced, must, therefore, be as 

 large, or larger, than these objects. The water should have about live per 

 cent of pure solution of lime added to it ; its temperature should be kept at 

 about seventy-two degrees. The objects to be dried in the sun. Journal of 

 Pharmacy. 



USEFUL APPLICATION OF AMMONIACAL CHLOPJDE OF ZINC. 



By dissolving equal equivalents of chloride of zinc and sal ammoniac, a 

 double salt, composed of these two substances, readily crystallizes in six- 

 sided prisms. This salt possesses the power of dissolving oxide of copper 

 and oxide of iron. It is, therefore, possible, by means of a concentrated 

 solution of the ammoniacal chloride of zinc, to polish rusty spots on iron 

 and copper. In tinning copper vessels, the solution of ammoniacal chloride 

 of zinc is of great advantage: the surface to be tinned is treated with it, and. 

 the vessel placed over a charcoal fire; then, when the surface appears per- 

 fectly bright, the tin is poured in, so that it may spread over the surface.* 

 This method is also applicable for coating with lead. Piiarmaceutisches 

 Central Blatt. 



OX THE EMPLOYMENT OF CARBONIC ACID IN CONNECTION WITH 

 HYPOCHLOKITE OF LIME FOR BLEACHING PAPER-STOCK. 



An apparatus, devised by Didot and Barrnel,of Paris, for introducing car- 

 bonic acid, prepared by burning charcoal, into the solution of hypochlorite 

 of lime (bleaching salt), while the latter is in contact with the fibre which is 

 to be bleached, is described in the Nov. (18-39) No. of Barreswil's Repertoire 

 de Chimie Applique'e, vol. i. p. 4-37. 



The carbonic acid, 011 being introduced into the solution of bleaching salt, 

 unites with the lime, thus setting free hypochlorous acid, the decolorizing 

 action of which is infinitely more energetic when it is at liberty than when 

 in combination with a base. 



This process, says Barreswil, is of extreme simplicity, and one is at a loss 

 to comprehend why it had not been sooner invented, in view of the fact that 

 each and all of its phases have been so long and so well known. 



In order to judge of the practicability of the new process in so far as 

 concerns difference of price, strength, and whiteness of the paper, and the 

 duration of the operations in the two systems (new and old) of bleaching, 

 comparative experiments were instituted, by the Messrs. Firmin Didot, upon 

 carefully assorted rags; the cost of the chemicals and labor, and the 

 amount o f time .required, having been exactly noted. After bleaching, the 

 pulp was converted into paper. The different papers were then carefully 

 tested. As the result of these experiments, it appeared that the new process 

 was more energetic and more rapid than the old method, au cMor? [,-fi/onire ?J 

 fiqni.de (with solution of bleaching salt), and that in many cases it is also 

 equally energetic \viih the process in which chlorine gas is employed. Over 



