SCIENCE IN THE INDUSTRIAL WORLD 



to describe. Generally speaking, however, the flame 

 that produces the best soot is a long, dull, red one, with 

 dark smoke issuing from the tip much such a flame, 

 indeed, as one sees in a smoky lamp. To keep this 

 condition as nearly as possible, the workman opens and 

 closes the "draughts" of the flue, these draughts con- 

 sisting frequently of bricks which he piles before the 

 opening or removes as the case requires. 



It is hardly necessary to say that in such a primitive 

 soot-gathering apparatus the maximum quantity of 

 high-quality soot is seldom obtained. In its perfected 

 successor, however, very little of the soot escapes. 

 Yet the difference between the two is one of construc- 

 tion, not of principle. The better apparatus has the 

 masonry flue supplied with necessary draughts with 

 which the amount of air admitted can be regulated to a 

 nicety. In place of the long wooden tube, a brick or 

 cement tube is used, and this in turn connected with a 

 high stack which is . supplied with a damper. The 

 pine root has been largely supplanted by resin for use 

 in such furnaces, and a product of better quality and 

 greater uniformity is obtained. However, even the 

 very best product obtainable from pine or resin is not 

 considered fine enough for the finer printing-inks, 

 such as those used for making half-tone illustrations. 

 These inks were made formerly from fatty oils or fish oils, 

 this variety of soot black being known as "lampblack" ; 

 but in recent years mineral oils and tar oils have been 

 found to be satisfactory substitutes. When vegetable 

 oils or fish oils are used, however, the cheaper and more 

 rancid they are, the larger is the yield of lampblack. 



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