VOL. LXIV.] PHILOSOPHICAL TRANSACTIONS. 495 • 



easy for the astringent matter to decompound the former, and produce an ink ; . 

 if this was the case, he suspected, that lime-water deepened the colour ofi 

 astringent and chalybeate mixtures, not so much by its action on the astringent, • 

 as on the chalybeate, the lime uniting with the superabundant acid, and leaving! 

 the iron with so much of the acid, as is necessary for the formation of an ink, 

 to be more easily attached by the astringent matter of the vegetable. But if this 

 theory was well founded, it followed, from analogy, that any substance, which 

 had a greater affinity with the vitriolic acid than iron had, would produce the 

 same effect, in some degree, as lime. To determine this: 



Exper. A. He took 2 vessels, containing equal measures of a strong astringent 

 liquor, composed of galls and logwood: into one vessel he put a small quantity 

 of pearl ashes; the other remained as a standard. Pieces of linen and cotton 

 cloth, after maceration in these liquors, were thrown together into a strong so- 

 lution of copperas; they were soon after taken out, and washed in cold water; 

 when dry, the pieces prepared in ashes were, all of them, much deeper than the 

 others. 



He made use of difi^erent kinds of pearl and pot-ashes, as well as of many 

 kinds of astringents; the ashes had the same effect, whatever astringent was 

 made use of, and the strongest alkali always produced the deepest colour; and 

 though ashes, used with an astringent, always gave a deeper black, than the 

 same astringent without ashes, yet logwood, which without ashes gave not so 

 deep a colour as galls with them, gave a much deeper black than galls with the 

 same addition. There was a remarkable difference, in this case, between lime 

 and ashes, in their effect on logwood; with lime it gave no blackness; but with 

 ashes, it produced a deeper black than any other astringent he made use of. 



Being desirous of trying the duration of colours, produced by astringents, in 

 which diflferent quantities of pearl-ashes had been dissolved; 



Exper. 5. In 2 pints of river water, he boiled 1 oz. of logwood, during 10 

 minutes; he then added half an ounce of Aleppo galls, and boiled them toge- 

 ther 10 minutes longer; the liquor having stood to cool, was decanted off, and 

 divided into 6 equal quantities. N° 1 remained as a standard; into N° 2 he put 

 6 grains of fine pearl-ashes; N" 3, 12 grains; N° 4, 18 grains; N° 5, 24 grains; 

 N° 6, 30 grains : to 6 drops of each of these liquors, he added 2 drops of a satu- 

 rated solution of copperas; N° 2 and 3 struck a deep black; N° 1 and 4 black, 

 but inferior to 1 and 3; N° 5, a brown black; N° 6, brown. 



From this experiment it appears, that N° 5 and 6 were spoiled by an over 

 proportion of ashes. Before seeing experiments, wherein it had been demon- 

 strated, that a quantity of acid enters into the composition of ink, Mr. C. ima- 

 gined the alkali decompounded the copperas too suddenly, and disengaged the 

 iron faster than the astringent matter could unite with it. But most probably 



