352 Experiments and Olservatlons on Lac. 



fies, twist the bag, and when a suffici?iit quantity has 

 transuded the pores of the cloth, lay it upon a smooth 

 junk ot" the plantain tree, and with a strip of the pli&itain 

 leaf draw it into a thin lamella; take it off while flexible, 

 for in a minute it will be hard and brittle*." 



The degree of pressure on the plaintain tree, regulates 

 (according to Mr. Saunders) the thickness of the'shell ; 

 and the quality of the bag determines its fineness and 

 transparency. 



Assam furnishes the greatest quantity of the whole of 

 the lac now in usef. 



Mr. Kerr (speaking of stick lac) observes, that the best 

 lac is of a deep red colour; for, if it is pale and pierced at 

 the. top, the value is diminished, because the insects have 

 left their cells, and consequently these can be of no use as 

 a dye or colour, but probably may be better for varnishes. 



The seed lac which 1 have examined, contained but little 

 of the colouring matter, and appeared (as I have already 

 observed) to have undergone some process of purification ; 

 but, of all the varieties, shell lac contains the least of the 

 tinging substance, as may well be expected, when the 

 iDode of preparing it is considered. 



It is remarkable, that although lac has been known and 

 imported into Europe, during so long a time that the date 

 cannot now be ascertained, yet it has but little attracted the 

 attention of chemists. 



The first chemist of eminence who mentions it, and the 

 only one who has subjected it to any thing like a regular 

 examination, is the younj;er Geoffroy, whose paper is pub- 

 lished in the Mem. de I'j^cad. de Paris for the year 1714J. 

 In this paper, Mr. GeoflVoy seems to have been chiefiy in- 

 di\ced to examine it on account of its tinging substance; 

 but he nevertheless has not neglected the subslance which 

 constitutes the cells. This he" considers to be a sort of 

 wax, very distinct from the nature of gum or resin. But 

 it is to be observed, that he formed this opinion, not so 

 much upon the results of chemical experiments, as upon 

 the cellular construction observed in the stick lac, which, 

 as he justly remarks, demonstrates it to be formed by in- 

 sects, alier the manner that the honeycomb is formed by 

 bees; and that it is not therefore, as some have supposed, a 



•Phil.Tran'-. 1781, p. i-g. t Phil. Trans J7S9, p. io(). 



I OSservations sur la Gomme Larqnc, it siir Ics r.utrcs Maticres ani- 

 m^lc: qui foLirnisse:it la Ttintucc dt Pourpie. Par M. GeuiLoy Icjeuoe. 

 M.'m. df r Acad. 1714, p. 121. 



jrum 



