206 ANNUAL OF SCIENTIFIC DISCOVERY. 



The whole was then placed under the receiver of an air-pump, and a 

 vacuum was formed. The alcohol soon acquired a marked viscidity, 

 and lost some part of its transparency. At a subsequent lecture, the 

 experiment was repeated with an apparatus composed of two concen- 

 tric cylinders, the interiors of which were filled with the above-men- 

 tioned paste. The double cylinder inclosed on each side the tube 

 containing the protoxide, and that containing the alcohol, and as be- 

 fore the whole was submitted to the action of the air-pump. When 

 the refrigerating substances were considered to have been almost 

 volatilized, the tube containing the alcohol was drawn out, and placed 

 in a horizontal position. The surface of the liquid remained for sev- 

 eral moments perpendicular to the axis of the tube, after which the 

 alcohol slowly regained its fluidity. M. Despretz considers that in 

 both cases the upper layer of alcohol was solidified, and that the 

 whole would have been had he continued the experiment a longer 

 time. The want of a further supply of the liquid protoxide prevented 

 him from pursuing the investigations further. Comptus Rendus, Jan. 

 29. 



GUN-COTTON. 



DURING the meeting of the French Academy, on Jan. 22, a discussion 

 arose with reference to gun-cotton, which is reported at length in the 

 Comptus Rendus, from which we translate the substance of some re- 

 marks by M. Morin. He stated that the very quality of great explo- 

 siveness, which has been put forward as the chief recommendation of 

 gun-cotton, is in .reality a great fault, which has already caused many 

 accidents. During the process of manufacture it cannot be raised to a 

 very high temperature, without great danger of explosion, as has been 

 proved in many cases; and even when only slightly heated, it ex- 

 plodes sometimes without any apparent reason. Gun-cotton cannot 

 safely be raised to more than about one quarter of the temperature 

 which powder will bear. In the using of the gun-cotton, also, much 

 care must be exercised not to get the charge too large, and in reduc- 

 ing its quantity the power is often too much decreased. By experi- 

 ment it has been found that cannon burst with a charge of gun-cotton 

 of about one fourth the quantity of powder necessary to burst them. 

 Again, a gun can ordinarily be fired with a medium charge of powder 

 from 25,000 to 30,000 times before it bursts, while even with a very 

 small charge of the gun-cotton a gun rarely stands more than 500 dis- 

 charges. All the means adopted to render the gun-cotton less ex- 

 plosive have been unsuccessful, except where they have been attended 

 with too great loss in the power. 



IMPROVEMENT IN SILVERING GLASS. 



THE object of this invention is to cause the silver to be deposited 

 from a solution of that metal upon glass in such a manner that a pre- 

 cipitate of silver will adhere to it, without any previous coating hav- 

 ing been applied. The mode of carrying out the invention is as fol- 

 lows : One ounce of ammonia, two of nitrate of silver, three of water, 



