298 Procefs for extra&ing a Gum from Lichens. 



The fcalded lichen is then to he put into a copper boiler 

 with a due proportion of water, fay three Scotch pints, or 

 two wine gallons, to every pound of lichen, and boiled during 

 four or five hours, adding about half an ounce or three quar- 

 ters of an ounce of foda or pearl-afhes for every pound of 

 lichen ; or, inftead of thefe falls, about half an Englifh pint 

 of volatile alkali. The boiling mould be continued until the 

 liquor acquires a confiderable degree of gummy confidence. 

 It is then to be taken out of the boiler, allowed to drain or 

 drip through a wire or hair cloth, or fearfe. The refiduum 

 to be put into a hair cloth bag or bags, and to be fqueezed 

 in a prefs fimilar to that which is ufed by the melters or 

 rinders of tallow. 



The firft boiling does not extract the whole of the gum. 

 The lichen fhould be boiled a fecond and even a third time, 

 repeating the procefs as above defcribed, diminifhing at each 

 procefs the quantity of water and the quantity of alkali, which 

 a little experience will foon point out. When three boilings 

 are employed, the gummy extract of the laft boiling fhould 

 be kept for the firfl boiling of a frefh batch of lichen. The 

 extract proceeding from the firfl and fecond boilings mould 

 be mixed together, and evaporated to the confluence necef- 

 fary for block or prefs printing. The evaporating veffels 

 fhould be of tin or thin lead, placed over a range of ftoves, 

 and moderately heated by fire or the fleam of water. It has 

 been neglected to flate, that before evaporating the gummy 

 extract to the confidence neceffary, it fhould be kept ten or 

 twelve hours, fo as to allow the fediment or dregs to fubfide. 

 The clear liquor may either be drawn oflby a fyphon, or the 

 dregs may be drawn off by a cock at the bottom of the 

 wooden vefTel ; the bottom of which fhould be made {loping, 

 higher at the back than the fore part, in order that the dregs 

 may run more completely off. The proportion of gummy 

 matter remaining in the dregs may be got off by mixing 

 them with a due proportion of boiling water, allowing the 

 liquor to clear, and proceeding as above directed, employing 

 this weak folution for boiling the next batch of lichen. 



The refiduum of the lichen, after the third boiling, con- 

 fifts of a matter fomewhat analogous to that of animal mat- 

 ter, together with a proportion of the fibrous matter of the 

 plant, ^From the animal matter a kind of foap may be made. 

 The procefs is as follows : 



Let a fmall proportion of pounded refin be difiblved by 

 boiling in a folution of alkaline falts. When the refin is 

 difiolved, put in a certain quantity of the refiduum of the 

 [fclh 1 Jiuiiiue the boiling uniil this, laft article is pretty 



well 



