82 



NA rURE 



[NOVEMUER 19, 1908 



Acheson finds th;it it is not always desirable to convert 

 the whole of the articles into graphite, but that if the 

 operation is stopped when a portion is still ungraphitised 

 they are stronger and less liable to fracture than when 

 they consist of pure graphite. 



It has already been mentioned that graphite of any 

 desired purity can be obtained by this process, it simply 

 being a question of how long the product is heated in 

 the furnace. When it is to be ground and used as a 

 lubricant it is necessary to make it of a higher degree 

 of purity than when required for many other purposes ; 

 but, however pure the graphite, there are certain difficul- 

 ties in employing it as a lubricant mixed with oil or water, 

 owing to its precipitating out very shortly after being 

 mixed with them. Although many attempts have been 

 made to get over this difficulty, it is only quite recently 

 that Acheson has been successful in doing so. In 1901, 

 when experimenting upon the manufacture of crucibles, he 

 found some difiiculty in obtaining clay which had good 

 binding qualities. He therefore commenced the study of 

 clays which are used in the manufacture of crucibles. It 



1 Graphi 



w.is noticed that .Xmerican crucible makers imported the 

 clay from Germany, because, although the clay has 

 practically the same chemical constitution as the American 

 product, it has a greater tensile strength and is more 

 plastic. Acheson then noticed that clays found at or near 

 to the place at which the felspar rocks are decomposed 

 are not so plastic or strong as when obtained at a distance 

 from their source of origin. It occurred to him that this 

 might be due to their containing vegetable or organic 

 extract matter. 



Experiments were therefore undertaken upon the action 

 of vegetable extract matter, such as tannin and plant 

 extracts, upon various clays. Remarkable results were 

 obtained, it being found that a weak and only moderately 

 plastic clay, after treatment w'ith a dilute solution of 

 tannic acid or extract of straw, increased in plasticity and 

 became much stronger. In some cases the increased 

 strength was as much as 300 per cent., and only 60 per 

 cent, as much water was required to produce a given 

 degree of fluidity. It remained suspended in water, and 

 would pass through a filter paper. Clay thus treated 

 Acheson called " Egyptianised," because the " Children 

 of Israel " used straw in making bricks. 



Now as clay so treated would remain suspended in 



water, it occurred to Acheson that perhaps the fine, 

 unctuous graphite' which he' succeeded in directly manu- 

 facturing in the electric furnace in iqo6 would also remain 

 suspended in water if thus treated. 



When disintegrated, graphite is treated with water con- 

 taining tannin, the weight of which was from 3 per cent, 

 to 6 per cent, of the graphite employed. The graphite 

 remains suspended in the water indefinitely, and passes 

 through a fine filter paper ; it is therefore in a semi- 

 colloidal condition. Graphite so treated Acheson calls 

 " dcftocciilated." To cause complete deflocculation and 

 the suspension of the whole of the graphite requires pro- 

 longed mastication in the form of a paste with water and 

 tannin, and after this mastication it is improved by 

 diluting with considerable water and allowing to remain 

 some weeks, with occasional stirring. The addition of a 

 very small quantity of hydrochloric acid causes fioccula- 

 tion and precipitation. 



The graphite, even after it has brrn flocculated, is in 

 so fine a state of division that when dried by evapora- 

 tion en masse it forms a hard cake. It is self-bind- 

 ing, like clay, and when dried 

 in the sun is like a black clod of 

 clay. 



This deflocculated graphite is a 

 splendid lubricator, and ma\' be 

 used in place of oil. It was tested 

 <in a shaft measuring 25/16 inches 

 in diameter, and running at 3000 

 revolutions per minute in a bear- 

 ing 10 inches long. On the same 

 sliaft a similar bearing was lubri- 

 cated with oil, and this ran much 

 the warmer of the two. If water 

 alone is used for lubricating, rust- 

 ing ensues ; no rusting takes 

 place with defloccul.-ited graphite. 

 Deflocculated graphite can also be 

 suspended in the dehydrated state 

 in oil. The two products come on 

 the market as " aquadag " and 

 " oildag " (d-a-g = deflocculated 

 .'\cheson graphite). 



.Aquadag has been found very 

 satisfactory as a cutting com- 

 pound in screw-cutting. It will 

 be readily understood that, while 

 preventing rust, the high specific 

 heat of the water permits high 

 speed of the machinery, and there- 

 fore increased output. One dis- 

 advantage of aquadag is the rapid 

 evaporation of the water ; conse- 

 quently, for general lubricating 

 purposes, oildag is of more value. 

 For automobile lubrication, for 

 stated to have proved much more 



exaipple, oildag 

 efficient than oil without graphite. 



F. M. P. 



THE F.-1L'.V.4 OF THE MAGELLAN i?£G/OJV.> 

 TN 1892-3 Dr. \V. Michaelsen conducted a zoological 

 ■'■ collecting expedition to the south end of South 

 America, and was remarkably successful as regards booty. 

 Descriptions of his collections began to appear in 1896, 

 and they are now gathered together in three substantial 

 volumes, each of several hundred pages. Dr. Michaelsen 

 gives a lively account of his journeyings, and Prof. Dr. G. 

 Pfeffer, of' Hamburg, who persuaded some of his 

 enlightened fellow-citizens to subsidise the expedition, 

 refers briefly to the general bearing of the various con- 

 tributions. It seems to us a matter for regret that there 

 is no adequate summation of the results of the expedition, 

 though we do not know what more Dr. Pfeffer could have 

 done within the limits allotted to him. It is certainly 

 I " Ergebnisse der Hamburger Magalhaensischen Samtnelreise iSos-gj. 

 Herausgegebcn vom Natlirhislonschen Museum zu Hamburg. Bd. 1., 

 Allgemeines, Chordonier. Echinodermen, und Coelemeralen. Bd. 11., 

 .i^rthropoden. Bd. iii., Eryojoen und Wilrmer. Net continuously paged ; 

 numerous plates (Hamburg : L. Friederichsen and Co., 1896-1907.) 



NO. 2038, VOL. 79] 



