1 5fr ' A'itf Procifs for making Vegetable Lain, 



this affinity ; but that lead, bifmuth, antimony, and zinc, produce the fame efFecl ; that it 

 takes place more fpeedily and completely with iron ; and that the contadt of all thefe metals 

 produces a very perceptible violet tinge in fuch infufions, as without this circumftance are 

 of a lively and decided red colour. 



That the green and acid part of fruits does not contain the colouring principle which is 

 difpofed to become red with acids ; and that the coloured part retains in combination^ 

 that portion of acid which isneceffaryto maintain the ftate of re-aiSlion that determines the- 

 fliade. 



That although this colouring principle is nxodified in certain vegetables fo far as to refift 

 acid or alkaline re-agents to a certain degree, as fernambouc with regard to acids, and turn- 

 fol with regard to alkalis, yet it rjiay be brought to this condition ; which feems to fliew thac 

 it is, if not eflentially yet at Icait originally, of the fame nature. 



That the metallic oxides are not all equally proper to feize and fix vegetable colours; 

 that fome among them appear to attack them with more facility, while others retain them 

 with very little power. 



Laftly, thtit the new metal called tungften, carried to the laft degree of oxygenation, which 

 has not hitherto been tried in this refpeft, has a decided advantage over all the other me- 

 tallic oxides i that it is capable of forming lakes of great value to painters, which perfeflly- 

 refift the proofs of lime-water, of acetic acid or radical vinegar, of hydro-fulphureous gas^ 

 and even to a certain point the oxygenated muriatic acid gas, that enemy of colours, which; 

 burns them fuddenly, and, according to the expreflion of Citizen Berthollet, reprefents in a few 

 inftants the combined action of air and light. "We fhall be lefs furprifed at this alTertion, 

 when it is recolleclcd that this is the only metallic oxide which eludes the folvent power of 

 the three mineral acids. 



The oxide of tungften eafiiy becomes charged with the colours of all vegetable matters. 

 I have hitherto found no more than one exception in the petals of nic-ago, of which I have 

 not been able to cxtradl the fine purple red, without being yet able to fufpedt the caufe of 

 this difference. 



In general, the lakes formed with this oxide become deeper inftead of fainter when they 

 are diluted. It is neccfiary to foften the fliade, I have remarked that they acquire ftili 

 more intenfity when the oxide has been previoufly rendered blue by boiling it in vinegar. 



One of our aflbciates, Citizen Vauquelin, being informed of the objeft of my refearches, 

 dire£led-my attention to aloes. Citizen dcs Fontaines had the goodnefs to procure me feveral 

 kinds I (hall fpeak only of that which bears the name of foccotrrne. I made experiments on 

 this plant, which is one of the moft rich in colour, though it does not exhibit the flighteft 

 appearance while the equilibrium of its principles is maintained by the energy of vegetable 

 life. The woody fibre, which is the external part, then fervcs as the covering of a very 

 vifcid matter, of a greenifh white colour, weakly acid ; but fcarcely has this matter been 

 expofed to the air before it afiumes a very lively red purp'e colour, which becomes very 

 abundant by the progrefs of fermentation. I have formed lakes of this matter with alumine, 

 oxide of tin, and the white oxide of zinc. None of them were comparable to that prepared 

 with tungften. 



1 do not doubt but that the oxide of this new metal may likewife be ufeful in the compo- 

 ition of colours for dyeing, at leaft for the dyeing of filks, which are not intended to with- 



ftaod 



