L. TECHNOLOGY. 473 



provements made, based upon the experience of the author 

 for many years past. In this paper attention is called to the 

 importance of the announcement, by Chevreuil, that the act 

 of drying of linseed-oil is due to the absorption of oxygen, 

 and that too long boiling retards the drying of oil instead of 

 hastening it. The practical application of this first point has 

 been the suggestion of various devices having for their object 

 the supplying of oxygen in greater quantity, in a given time, 

 than would naturally be taken up from the atmosphere. An- 

 other point of progress in regard to the manipulation of this 

 substance is said to consist in the discovery that the high 

 temperature formerly employed in boiling oil is unnecessary, 

 and that the work can be done to much better advantage by 

 the use of steam, with a great improvement in the color of 

 the oil and in its practical value. 



According to our author, a valuable application was made 

 of the theory of the absorption of oxygen in drying by Fara- 

 day, some years ago, when consulted as to the possibility of 

 hastening the drying of printing-ink so that the work might 

 be milled or plated (pressed between sheets of zinc) with less 

 delay after printing, a fortnight being the usual time required 

 before this process can be attempted. At Professor Faraday's 

 suggestion, binoxide of manganese was added to the ink, with 

 such effect that for thirty or forty years this substance has 

 been used with perfect success for accomplishing the desired 

 object, at the Queen's Bible Office, where the work, if neces- 

 sary, is milled in three days after printing. To get the bi- 

 noxide in a state of division sufficiently fine to be mixed with 

 printing-ink, Faraday devised a series of washing receptacles, 

 like successive stairs, the fine particles passing on to the low- 

 er vessels being longer suspended than the coarser a simple 

 yet ingenious arrangement, which enabled the ink to be work- 

 ed without any risk to the plates or forms from grit. 1 A, 

 April 28,197. 



TRANSPARENT GREEN VARNISH. 



A beautifully transparent green varnish is made by tak- 

 ing a small quantity of Chinese blue, with about twice the 

 amount of finely-powdered chromate of potash, and stirring 

 these in copal varnish thinned with turpentine. A thorough 

 grinding of this mixture must be made for the purpose of in- 



