478 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



lowing it to remain for some time, it is said that the attain- 

 ment of the desired result will be much facilitated. 6 C, v., 

 40. 



METALLIC SOAP. 



Metallic soap in linseed-oil is highly recommended for coat- 

 ing canvas for wagon-covers, tents, etc., as being not only im- 

 jjermeable to moisture, but remaining pliable for a long time 

 without breaking. It can be made with little expense, as fol- 

 lows : Soft soap is to be dissolved in hot water, and a solu- 

 tion of copperas (sulphate of iron) added. The Sulphuric acid 

 combines with the potash of the soap, and the oxide of iron 

 is precipitated with the fatty acid as insoluble iron-soap. 

 This is washed, and dried, and mixed with linseed-oil. The 

 addition of dissolved India-rubber to the oil greatly improves 

 the paint. 10 C\ v., May, 1871,60. 



WATER-PROOF STARCH. 



A patent has been recently taken out in France for the 

 preparation of a finish, or starch, for vegetable tissues, yarns, 

 cloths, etc., which is not soluble in water, and which, there- 

 fore, when once applied, will remain throughout several suc- 

 cessive washings. In this case, the articles in question are 

 properly starched, and then passed, at a temperature of about 

 60 Fahr., through a bath of chloride of zinc, by means of 

 which such a change is produced in the fibre and the starch 

 that the latter resists the action of the water in the most 

 thorough manner. A bath of three parts of sulphuric acid 

 and one of water may, it is said, be used instead of that of 

 chloride of zinc. The liquid is to be placed in a trough, in 

 which a revolving barrel is immersed almost to its axis, and 

 above which is a roller which is moved in the opposite direc- 

 tion by the turning of the lower one. Between the two the 

 material to be impregnated is passed, being moistened from 

 below by the bath, and, in passing between the two, receiv- 

 ing the necessary pressure. If the material be heavy, the 

 barrel lies entirely in the bath, aud a pair of rollers fixed 

 above it is used to press out the superfluous liquid. The ar- 

 ticles are carried directly from the trough into running wa- 

 ter, from which they are to be removed, pressed out, and 

 dried. 5 C, xvi., 127. 



