ON DRAWING, WRITING, AND MEASURING. 99 



Ivory, and prepared ass's skin, are sometimes employed for writing with a 

 black lead pencil; for slates, a pencil of a softer kind of slate is used. The 

 ancient mathematicians usually constructed their diagrams on sand for the in- 

 struction of their pupils. 



Pens of 'goose quills, swan's quills, or crow quills, were known as early as 

 the seventh century : in Europe they have generally superseded the reeds, 

 which were employed for Avriting by the ancients: but in India, reeds, canes, 

 and bamboos, are still in use. In China a hair pencil is used instead of a pen. 



The inks of the ancients arc said to have been made of a carbonaceous sul)- 

 stance, and the modern Indian ink owes its blackness to similar materials. 

 Common writing ink consists of a gallate of iron, suspended by means of a 

 little gum; the sulfuric acid, which remains mixed with it, is probably of no 

 consequence to its blackness. It has been observed, that an abundance of 

 the gallic acid produces a much blacker colour, than is obtained where this acid 

 is used in a smaller proportion. Mr. Kibaucourt's method of making ink, is 

 to boil eight ounces of galls, and four of logwood, in twelve pounds of water, 

 until the quantity is reduced to one half; and, having strained the decoction, 

 to add to it four ounces of sulfate of iron, one of sulfate of copper, three of 

 gum arable, and one of sugar candy. But for ordinary purposes, it is sufficient to 

 infuse three ounces of galls for a day or two in a pint of water, and to add to 

 it an ounce of gum arable, half an ounce of green sulfate of iron, or cop- 

 peras, and a drachm of sulfate of copper, or blue vitriol, or even a much 

 smaller quantity of gvim and of copperas, if a very fluid ink is required. The 

 sulfate of copper produces a durable stain, but it does not immediately add 

 to the blackness of the ink: its principal use is to counteract the tendency of 

 the ink to become mouldy. Sometimes a mercurial salt is employed for the 

 same purpose, and a little cotton, if the inkstand is too open, is also useful in 

 preserving the ink ; but the addition of spirits is often insufficient, and is liable 

 to make the ink run. 



It has been proposed to use inks of diffiL'rent colours for indicating different 

 lumibcrs; so that by ten kinds of ink applied in different ways, any numbers 

 at pleasure might be expressed. Thus, in making an index of the words of an 

 author, each page might be readily covered with lines of different colours 



