Prof. E. Wartniann's third Memoir on Induction. 261 



cotton may exceed gunpowder in its explosive force still re- 

 mains to be ascertained, and this of course forms an important 

 element in the calculation. Other processes may be already 

 known, or may be hereafter discovered, calculated to reduce 

 the expenses of the formation of the so-called gun-cotton, 

 but it must be still borne in mind that an enormous quantity 

 of oxygen, amounting to 45 parts in every 100 parts of gun- 

 cotton produced, must be obtained from some extraneous 

 source for combination. 



Many other vegetable fibres may be substituted for cotton ; 

 but as far as a few experiments which I have made, it appears 

 they do not possess the explosive force of cotton. In a trial 

 upon flax, I found that 50 grs. increased in weight to 72 grs. ; 

 the explosive force was feeble ; this was the case with sawdust 

 similarly prepared ; but it is possible that this latter form of 

 impure lignin may eventually be of more importance than it 

 appears at present. 



Fifty grains of deal sawdust dried at 212° were first waslied 

 with dilute muriatic acid and then with dilute caustic alkali; 

 they were found to have lost 6 grs. after washing and again 

 drying. The 44 grs. remaining were steeped in the mixed 

 acids for about five minutes, then washed and dried ; they 

 increased to 58*7 grs. The acids were examined by carbonate 

 of soda in the manner before detailed, the sawdust was found 

 to have neutralized 22*90 grs. of soda, equal to 38*65 parts 

 of nitric acid, or 66*66 of nitric acid for every 100 parts of 

 gun- sawdust. This gun-sawdust flashed off readily, but with 

 less rapidity than gun-cotton, leaving a small carbonaceous 

 residue. 



The difference in quantity of nitric acid taken up by the 

 sawdust and the cotton is no doubt owing to the fonner being 

 a much more impure form of lignin than the latter. 



XLIV. Third Memoir on Induction. 

 Bj/ Prof. Elie Wartmann*. 

 [With a Plate.] 

 § VIII. Does electro-magnetic induction affect luminous radia- 

 tions otherwise than hxj causing their i^lane of polarization 

 to rotated 



80. IVTR- Faraday has recently stated that a rotation is 

 -*-'-■- impressed on the plane of polarization of luminous 

 • Comtmmicsiteil by the Autlior, havinfj been read before the Vaiidois 

 Society of Natural Sciences on the 20th of May 1846 (see Jijillclins, torn. ii. 

 |»|). 58, Gl,70, 75 and U8> It is a scuiicl to those which have been |)ublished 

 inthcl'iiil. Mag. vol. xxv. ]>. 2()G, and vol. -Nxvii. p. 347, and in tha Anliivcs 

 dcPElcctiicitc, tome iv.p. 34, and tonic v. p. 440. 



