On making Artificial Pearls. 231 



but instead thereof, suspend the pearly particles in a solution of 

 isinglas, well clarified, and which they drop into the bulbs, 

 and then turn them in all directions, in order to spread it equally 

 over the interior surfaces. There can be no doubt, that in this 

 mode of applying the pearly mixture, the same success will be 

 obtained as in the before mentioned process, and that it will 

 afford a layer of the same thinness and brilliancy. 



It is important, to succeed in the perfect imitation of pearls, 

 that the glass bulbs or pearls employed should be of a slight 

 bluish tint, opalized, and be also very thra ; and likewise, that 

 the slass should contain but little potash, or oxide of lead. In 

 each manufactory of these artificial pearls, there are workmen 

 exclusively employed in the blowing of these bulbs, and which 

 requires a great dexterity to succeed well therein, — a dexterity, 

 indeed, which can only be acquired by long practice. 



The French manufacturers of these artificial pearls have at 

 leno'th attained a degree of perfection before unknown. We 

 must add, that the bulbs are finally filled up with white wax. 



On Improvements in Black Writing Ink. By John Bostock, 

 M. D. F. R. S., &c. 



When the sulphate of iron, and the infusion of galls, are add- 

 ed together for the purpose of forming ink, we may presume 

 that the metallic salt or oxide enters into combination with at 

 least four proximate vegetable principles, viz. Gallic Acid, Tan, 

 Mucilage, and Extractive Matter,— all of which appear to enter 

 into the composition of the soluble parts of the gall-nut. It has 

 been generally supposed, that two of these, gallic acid and the tan, 

 are more especially necessary to the constitution of ink ; and 

 hence it is considered, by our best systematic writers, to be es- 

 sentially a tanno-gallate of iron. It has been also supposed 

 that the peroxide of iron alone possesses the property of forming 

 the black compound which constitutes ink, and that the sub- 

 stance of ink is rather mechanically suspended in the fluid than 

 dissolved in it. 



