air. hatchett's experiments, &c. 45 



In all the above experiments there was a large furface of 

 contact, and the electrometer only was ufed; but in thofe made 

 by Cavallo and others who had a very fmall furface of contadt, 

 electrical figns could not be made to appear without the help 

 of doublers, multipliers, &c. of electricity. I therefore think 

 there can be no doubt about the feparating the metals from con- 

 tact being the caufe of their appearing. 



If you think the above worthy of a place in your Phliofophi- 

 cal Journal, you will very much oblige me byinferting it therein. 

 I am your obedient humble fervant, 



WM. WILSON. 



XII. 



Analytical Experiments and Obfervations on Lac. By Charles 

 Hatchett, Efq. Partly abridged, but chiefly extracted 

 from the Philofophical Tranfa&ions for 1804<, by W.N. 



IT is uncertain at what time the ufeful fubftance, called Lac, ufes of lac pe- 



firft became known in Europe. It has long been ufed by the cullar t0 In<Ka « 



Indians for purpofes different from thofe to which it is applied 



in Europe. In particular as Mr. Wilkins informed the author, Aqueous folution 



they diflblve (hell lac in water by the addition of a little borax, b ? bo , rax affords 



an ink. 

 and by adding lamp black or ivory black, they obtain an ink, 



not eafily affe&ed by water, when dry. 



The natural hiftory of lac, which is the nidus of the coccus Natural hiftory 

 or chermes lacca, has been detailed by Mr. Kerr , Mr. Saun- of lac * 

 ders, and Dr. Roxburgh, in the Philofophical Tranfa&ions 

 for 1781, 1789, and 1791. It is difiinguifhed into four kinds, Four kinds. 

 of which, however, only three are commonly known in com- 

 merce, viz. ftick lac, feed lac, and fhell lac; the difference 

 of thefe, with that of the fourth, called lump lac, is as follows. 



1 . Stick lac, is the fubftance or comb in its natural ftate, x . Stick lac. 

 incrufting fmall branches or twigs. 



2. Seed lac, is faid to be only the above, which has been fe- z. Seed lac, 

 parated from the twigs, and reduced into fmall fragments; but 



I fufpeft it to have undergone fome other procefs, as I have 

 found the beft fpecimens to be very confiderably deprived of 

 the colouring matter.* 



3. Lump 



* Mr. Wilkins informs me that the crude lac, as it is taken from 

 the branches and twigs of the trees, is ufually deprived of its colour. 



ing 



