126 Proceedings of the British Association. 



Prof. Grove wished to make some inquiries relative to the suppos- 

 ed existence of a new principle in connexion with light, which was 

 regarded by Mr. Hunt and others as the active chemical agent, to 

 which was to be ascribed all the phenomena of photographic action, 

 and the most genial influence on the growth of the young plant. — 

 Mr. Hunt explained that the luminous calorific and chemical spectra 

 were capable of producing extremely different effects. That the light 

 coming from the sun was not at all equal in quantity to the heat ; and 

 that that element was much less than the amount of chemical power. 

 He showed by diagrams, that the quantity of chemical power increas- 

 ed in the spectrum as the light diminished, and that when the light 

 was at a maximum the chemical action was at a minimum. It was 

 also stated, that by the use of absorbent media, light of great inten- 

 sity could be obtained, which possessed scarcely any chemical power ; 

 and on the contrary, that this chemical principle of the solar beam 

 could be obtained in the same way with but a very small amount of 

 light. 



Dr. Bateman described Mr. Phillips's method of discovering Adul- 

 teration in tobacco. — The basis of this plan is the ascertainment and 

 comparison of the relative proportions of soluble and insoluble matter 

 in tobacco ; water being the solvent. Numerous experiments have 

 proved that every kind of vegetable matter has a determinate portion, 

 which is soluble in water; thus rhubarb-leaves range from 18 to 26 

 per cent., and horse-radish, lettuce, oak, elm, and many others, have 

 their definite limits. This amount, with reference to tobacco, in no 

 case exceeds 55 per cent, of the tobacco : and thus if tobacco be 

 adulterated with matter soluble in water, the extractive or soluble 

 part is increased, whilst the ligneous and insoluble matter are cor- 

 respondingly decreased. A sample of genuine tobacco, by careful 

 manipulation, affords 50 per cent, of soluble matter, and when 

 another portion of the same tobacco has been mixed with 1 5 per cent, 

 of soluble matter, the sophisticated article can contain only 85 per 

 cent, of tobacco ; and it would be found by experiment to afford to 

 water 57.5 of soluble, and 42.5 of insoluble matter, thus affording 

 proportions for calculating the actual amount of adulteration intro- 

 duced, 



