218 DURABLE AftD SUPERIOR LAKE. 



and fettle after be differed to fland, without the addition of the alkali, aeon* 

 the alum was fiderable precipitation will take place, which will be of a dark 



added it affords * « ~_ _ . . 



a dull red f edi_ du " red - The remaining liquor, if again heated, will, by the 

 ment. admifiion of the alkali, produce a rofe-coloured precipitate of 



and the remain- . '. . * r 



ing fluid if abeautihil tint, but wanting in force and depth or tone, 

 heated and pre- This is the procefs recommended by Mr. Watt, in his 

 alkali Affords a Effay on Madder, in the Annals de chymie, Tome 7 ; and this 

 fine but not latter colour is what may perhaps, with propriety, be called 



hWa 1 t?s e \oTe 1 fs S . Madder Lake - But ' aIthou g h th e lighter red may be ex* 



cellent for many purpofes, yet I confider the colour produced 



by the union of the two colouring matters, as given in the 



firft procefs, as far preferable for general ufe, being of a very 



beautiful hue when ufed thin, and poffeffing unrivalled depth 



and richnefs either in oil or water, when laid on in greater 



body. 



Lefs alumcaufes If but half an. ounce of alum be added to the two ounces of 



the fecond pre- the root tlie faft precipitate will be nearly fimilar to that 



cipitate to be • , , , >/-''. i i 



lei's in quantity, when an ounce is employed; but. the lecond, or lake pre- 

 but richer. cipitate, will be lefs in quantity, and of a deeper and richer 



tint. In this cafe the whole of the colouring matter, as be- 

 fore obferved, is certainly not combined with the alumine ; 

 for, on adding more alum to the remaining liquor, a pre- 

 cipitate is obtained of a light purplifh red. In this procefs^ 

 when two ounces of madder and an ounce of alum are ufed, 

 the fir ft precipitate has about 20 per cent, of alumine, and 

 the fecond, or lake precipitate, about 53 per cent ; but the fe 

 proportions will vary a little in repetitions of. the procefs. 

 Procefs 3. When Procefs 3. If the madder, inftead of being wafhed and 



the wa flung is triturated with cold water, as directed in the foregoing procefs, 

 performed by , , . _, . r ...... . 



Doiiing inftead be treated in exactly the tame manner with boiling water; the 



of cold water, colour obtained will be rather darker, but fcarcely of fo good 



neithe^fo good a tmt '> and the >"efiduum of the root, however carefully preffed 



nor fo plentiful, and wafhed, will retain a ftrong purplifh hue; a full proof 



that fome valuable colour is retained in it, probably fixed 



in the woody fibre by the action of heat. Mr. Watt, in his 



excellent treat ife on madder above mentioned, obferves* 



that cold water ejetradis the colour better than hot water ; and 



I have reafon to fufpect, that a portion of that colouring 



matter, which produces the bright red pigment, diftinguifhed 



before by the name of Madder Lake, remains attached to 



the root, when afted on by boiling water. 



Procefs 4. 



