IH- Mr. Reid on Writing-ink, and on the Effects 



quired lo produce" the deepest intensity of colour is exactly 

 three times as great as the quantity of protosulphate which 

 is required for making ink. This salt is recommended for 

 this purpose by Berthollet, but he has not given all the cir- 

 cumstances which it is necessary to attend to. 



Since the time of Dr. Lewis, logwood has been used as an 

 ingredient in making ink, by which an increase of colour is 

 effected at an inconsiderable expense, without in any consider- 

 able degree injuring the properties of it. As the phaenomena 

 which logwood presents with sulphate of iron are in some re- 

 spects peculiar, it is proper to allude to them in this place. A 

 solution of logwood when recently made, absorbs oxygen from 

 the air; and accordingly as it has absorbed more or less, there 

 is a difference in the colour of the compound which results with 

 the sulphate. With the decoction when recently made it 

 forms a compound of a greenish-blue colour ; when it has been 

 exposed for some time (a day or two) to the air, a blue com- 

 pound results ; and when it is saturated with oxygen, the com- 

 pound is of a brownish-black colour. There is no increase 

 of colour along with these changes ; on the contrary, the blue 

 compound has a much deeper as well as a much richer colour 

 than the last. A precipitate falls down in each case, and is 

 equally as copious in the last as in the first instance. It cannot 

 be used alone, therefore, for making ink, and ought not to be 

 used in more than a certain proportion along with galls or 

 gallic acid. When galls are used, the proportion is usually thi'ee 

 parts of galls and one and a half of logwood ; and the latter 

 ought not to exceed this quantity. Wlien gallic acid is used, 

 one part of it may be added to one and a half of logwood. 



In making ink with galls without the atldition of logwood, 

 the following directions may be observed: 



Take of galls, one pound. 



sulphate of iron, three ounces sixty-four grains. 



gum, ditto ditto 



water, three quarts. 



Boil the galls, when bruised, with three pints of water till a 

 quart of decoction remains ; pour it off, and add the remainder 

 of the water, and again boil till a (juart remains. Mix both 

 decoctions and dissolve the other ingredients in it; let them 

 stand for twenty-four hours, and pour off the fluid ink from 

 the precipitate, when it may be kept for use. 



If it should be wished to convert the tannin of the galls into 

 gallic acid, a decoction may be made in the manner above di- 

 rected. Let it stand exposed freely to the air for ten days, 

 agitating every day for a ^ew minutes two or three times a day. 

 By this means it may be converted into gallic acid; and as it 



thereby 



