VOL. XLIV.] PHILOSOPHICAL TRANSACTIONS. 211 



the assistance of fire. But the fire here spoken of is not great enough to dis- 

 solve their constituent parts, but only such as may affect the external parts of 

 their texture, and that but gently ; so that the process here mentioned is only 

 drying or roasting. For it is not the watery or the saline part in bodies which 

 is torrefied, but the oleaginous, with which many vegetables, and most animals, 

 abound. 



The white flesh of animals, such as that of chickens, becomes a phosphorus 

 by roasting, as well as the tendons, and whatever parts of animals become gluti- 

 nous by boiling, such as carpenter's glue, ising-glass, to these may be added 

 cheese. Bones, though they imbibe light without any preparation, have that 

 property in a much greater degree when burnt, and their luminous appearance is 

 much more lively. But roasting has not this effect on feathers, hoofs, horns, 

 or whites of eggs. The same operation which produces several phosphori from 

 the animal kingdom, gives also several from the vegetable. Thus, by gently 

 toasting gums, as myrrh, gum tragacanth, and others, appear luminous, though 

 different in degrees: and this light is clear, in proportion to the gentle evapora- 

 tion of their aqueous parts. By this treatment nuts of every kind, pulse, corn, 

 coffee-berries, meal, bread, and wafers, also become phosphori. Turpentine, 

 amber, and some resins, require more fire before they imbibe light ; so that you 

 must divest them of their acid, and their light ethereal oil, to make them appear 

 luminous. But here great care must be taken that they boil no longer than 

 from being white they turn yellow; for by proceeding longer, your labour 

 is lost. 



It is necessary to be acquainted, that those phosphori which are produced by 

 torrefaction, soon lose their power, which perhaps neither time, nor a thorough 

 dissolution of their parts, can deprive the natural ones of. In general, as long 

 as the phosphori, gained by torrefaction, preserve their power, their light is 

 more sharp and striking, but the natural more weak. But those that are gained 

 by calcination, and Baldwin's Phosphorus, seem to possess both the striking 

 light of those gained by torrefaction, and the weaker light of the natural phos- 

 phori : the last they preserve a long time, but the former is lost by degrees much 

 sooner. The well calcined ashes of plants, or rather their terrestrial parts, 

 remaining after the solution of their fixed salts by washing, and neutral salts, 

 continue phosphori after many years. So that, as far as we can judge, the lumi- 

 minating power which is gained by calcination, though not so intense, continues 

 perpetual ; whereas that gained by torrefaction always decreases, and in a very 

 little time is no longer visible. Some even, by this method, continue to imbibe 

 light much longer than others. Gum Arabic, which continues longest, lasts 6 

 days; bread, not one; and coffee, only a few minutes. However, at any time, 

 by a fresh torrefaction, you may recover these languid phosphori ; in which pro- 



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