1 62 Management of Light in Illumination. 



in melted tallow or melted wax, heated very hot, in 

 order more effectually to expel the air and moisture. 



Wicks for lamps may be prepared by immersing 

 them in hot melted wax, instead of using melted tallow 

 for that purpose ; and many persons who manage their 

 lamps themselves would, no doubt, prefer wax, on 

 account of its greater cleanliness; but, having tried 

 both these substances, I have not found that the wicks 

 which had been prepared with wax burned better than 

 those prepared with tallow. 



As dust, and in general every species of soil, is very 

 injurious to a wick, it is necessary that those which are 

 to be prepared be well washed and dried before they 

 undergo this operation. 



As oils that are purified by means of the sulphuric 

 acid always retain a certain portion of the acid, not- 

 withstanding all the pains that are taken to separate 

 and remove it, if that residue of the acid attacks the 

 wick and injures it, so as to spoil it entirely if left for 

 a considerable time in the oil, as is generally supposed; 

 as either the tallow or the wax used in preparing the 

 wick will effectually preserve the cotton from the acid 

 till it shall have been displaced by the oil, on being 

 melted in consequence of the lamp being lighted, — it is 

 evident that this mode of preparation must be useful 

 as a preservative against the attacks of the acid, espe- 

 cially when a lamp filled with oil remains some time 

 without being lighted. 



The corrosive effects of this acid are so injurious to 

 the burner, especially at its extremity where the heat is 

 considerable, that the burner of an Argand lamp sel- 

 dom lasts more than two years. To remedy this evil 

 I have lately given directions for the upper end of the 



