We refumed. 



30 SUBSTITUTE FOR GUKt-AK^BlCT. 



matic colours, more or Icfs changed by black ; and that the 

 tints of the fliadows obferved are always complementary to 

 each other. 



3rf, That the fliadows produced on a pafteboard illuminated 

 by artificial lights, are reddifli and bluifti, more or lefs dee'p ; 

 and that very probably the bluifti and reddifli tints of the 

 fliadows depend on the proportions of hidnogen and carbon 

 in the combuftible bodies. ii4 '■ ^ 



Thefubjeato We purpofe, if the Inftitute judges this Tubje6i worthy ot 

 their attention, to make known, in other memoirs, the expe- 

 riments we have made to determine the different caufes which 

 contribute to form coloured fliadows in every particular cir- 

 cumftance. 



V. 



Account of the Preparation of the Hyacinthus nan fcriptus, or 

 coffunon Blue-Bell, as a Suhfiitute for Gum-Arabic. In m 

 Letter from Mr. Thonas Willis of Lime-Street, London, com- 

 municated to Charles Taylor Efq, Secretary to the Society of _ 

 Arts *. 



SIR, 



b'^MT^Delux ^ HAVE obferved in the Appendix of the lafl Monthly 

 refpeftinggum Review, in their Report of the Chemical Annals, No. 115, 

 from the hya- ji^^^ mention is made of a letter froni Mr. Deyeux, to the 

 fcriptua. authors of the Annales de Chimie ; in which an account is 



given that a gummy fubftance had been difcovered, by Mons. 

 Deyeux, to be contained in the bulb of the plant called hya- 

 cinthus non fcriptus ; and that the reviewers only fay, " This 

 " article does not at prefent require any further notice than 

 annunciation." As I know. Sir, your benevolent difpofition 

 in promoting and encouraging the arts, the fciences, and 

 manufaflures of this kingdom, I beg leave to offer the follow- 

 ing obfervatlons on the above-mentioned article, which I think 

 a fubjedl proper to lay before your mofl excellent Society, 

 and which I have no doubt may become of national utility. 



♦ Exlraflcd from the Society's Memoirs from page 202{ The 

 filver raedal was adjudged to this Communication. 



4 In 



