April 25, 191 8] 



NATURE 



H7 



In response to an appeal from the Admiralty, 

 the Royal Astronomical Society is now sending- 

 round a circular to representative astronomers 

 and societies in our own, the Allied, and neutral 

 countries. This, after a brief resume of the cir- 

 cumstances, enumerates the chang-es in the 

 almanac that would be involved if the new system 

 were adopted, and invites suggestions and 

 criticism. It is thought that 1925 is the earliest 

 date that is practicable for making the change, 

 since the almanac goes to press several years in 

 advance. It is proposed that the reckoning by 

 Julian days shall still begin at Greenwich noon, in 

 consequence of the numerous ephemerides of vari- 

 able stars that have been drawn up on this 

 system ; this would afford a means of relief to 

 those astronomers who dislike the change; by 

 dating their observations in Julian days, instead 

 of calendar dates, they could continue to keep 

 their nights undivided. 



It is hoped that the change, if made, will be 

 adopted throughout the astronomical world, so 

 that an interval is wisely being left for full ventila- 

 tion of the subject. Some have hopes that the 

 change might be accompanied by the introduction 

 of twenty-four-hour reckoning by the general 

 public; this system has long been in use in Italy, 

 and leads to a great simplification of time-tables 

 of railways, tides, etc. It does not necessarily 

 involve the use of new clocks with twenty-four- 

 hour dials. It suffices to use the present dials, 

 merely inserting i3h. to oh. inside the figures 

 ih. to lah. In fact, many prefer this system, 

 since the hours on a twenty-four-hour dial are in- 

 conveniently close. A. C. D. Crommelin. 



THE RECOVERY OF POTASH FROM 

 BLAST-FURNACE GASES. 



THE sources of potash were described by Sir 

 Edward Thorpe in an article in Nature of 

 January 3 (p. 344). One of these sources has been 

 the subject of study by Prof. R. A. Berry and 

 Mr. D. W. McArthur, who have published the 

 results of their investigations in a paper read 

 before, and discussed at, a meeting of the West 

 of Scotland Iron and Steel Institute. These in- 

 vestigators have studied in particular the possi- 

 bilities of recovering potash from the blast- 

 furnace gases obtained in Scottish practice, with 

 the view of obtaining information as to how far 

 these may be expected to constitute an economic 

 source of supply, when the restrictions imposed 

 by the war no longer hold. 



That the dust deposited from blast-furnace and 

 kiln gases contains potash salts has long been 

 known, and in 1884 Barclay and Simpson, of the 

 Harrington Ironworks, Cumberland, took out a 

 patent for the recovery of salts, and especially 

 potash salts, from coke-fed furnaces. The most 

 considerable investigation, however, on this sub- 

 ject is that by Wysor, of the Bethlehem Steel 

 Company, U.S.A., who found that the dust which 

 collected at the bottom of the stone chequer-work 

 in the stoves and gas-fired boilers contained 

 15 per cent, of water-soluble potash (KoO). Fur- 

 NO. 2530, VOL. lOl] 



ther, he drew up a balance sheet to show the 

 amount of potash charged into the furnace and 

 the percentage recovered. His conclusion was that 

 the greatest losses occurred in the primary and 

 secondary washers, constituting some 56 per cent, 

 of the whole, while 20 f>er cent, was carried off 

 in the slag; further, that less than i per cent, of 

 the potash charged was recovered in the dust 

 alluded to. In igi6 a Cottrell plant for electro- 

 static precipitation was installed, and it was found 

 that practically all the dust could be precipitated. 

 About 22'4 lb. of potash were charged per ton of 

 pig-iron produced, and after deducting the amount 

 contained in the slag and the dust-catcher, about 

 15 lb. per ton of pig-iron appeared to be left in 

 the gases, which were then recoverable in the 

 Cottrell plant. 



The average potash content of the American 

 ores is about i per cent., and as the production of 

 iron in the United States in 1916 was nearly forty 

 million tons, if Wysor 's figures are correct the 

 flue-dust from the furnaces should constitute a 

 very considerable source of supply. 



As the authors point out, the problem in Scot- 

 land is different : first, because coal, and not coke, 

 is the fuel generally used, and secondly, because 

 the ores contain rather less potash. With 

 coke-fired furnaces the gases are not washed, 

 but are led from the catchers direct to the stoves 

 and boilers. In coal-fired furnaces, however, 

 a considerable amount of tarry matter is pro- 

 duced, whereas the dust deposited is relatively 

 very small. The problem of recovery is therefore 

 different. The potassium is present in the ore, 

 principally, no doubt, in the form of silicate. This 

 reacts at the high temperature of the furnace and 

 forms other compounds, for, as the dust analyses 

 show, chlorides, sulphates, and carbonates were 

 the principal acid radicals present. It is well 

 known, further, that potassium cyanide is 

 formed in certain regions of the furnace, 

 but decomposed in others. At the high tem- 

 perature these potassium salts are vaporised ; 

 they condense in the cooler parts of the furnace as 

 fine dust particles, and are carried along with the 

 dust from the fuel and the ores. The first particles 

 deposited are the heaviest, and these are caught 

 in the dust-catcher, in the form of a coarse, black 

 powder; deposition also occurs on the main tube, 

 and these two constitute the tube cleanings. The 

 heavy, tarry matter separates principally in the 

 condensers and carries with it much of the fine 

 dust ; the gas then passes to the water scrubbers, 

 which retain the rest of the tarry matter and most 

 of the remaining dust. Any mineral matter still 

 retained is caught in the stove and boilers, 

 . The authors have received and analysed samples 

 of these deposits and liquors from various 

 plants in Scotland, and have determined their 

 potash content. Nine samples of flue-dusts were 

 examined : eight from coal-fired furnaces and one 

 from a coke-fired furnace. The highest yield of 

 dust in the former was only at the rate of 21 tons 

 per annum, as against 300 tons for the latter, and 

 the water-soluble potash averaged 8"86 per cent. 

 The percentage of ash in the tube cleanings varied 



