106 



SCIENCE. 



[Vol. I., No. 4. 



and still the results were unsatisfactory. It gradually 

 became apparent that what was wanted was surface, 

 and not volume. The iron pipes before described 

 not having been affected, there were introduced into 

 the flue sheet-iron plates hung vertically. Four of 

 these i^lates were at first put in; but the results were 

 so immediate and so gratifying, that the number was 

 Increased to six, with still better effect. The conclu- 

 sion was at once jumped at, that the flue would stand 

 all the plates that could be put into it ; and accord- 

 ingly seventeen plates were introduced, having a 

 space of 10 cm. between them. It was then discov- 

 ered, that nearly all of the material carried off me- 

 chanically was thrown down near the furnace, and 

 that volatilized was deposited a little farther on. 

 These results having been reached, the difficulty was 

 to keep these deposits where they were, and to pre- 

 vent them from being carried off by the immense 

 draught in so long a flue. This last obstacle was sur- 

 mounted by placing transverse sheets of iron in the 

 bottom. When the deposits reached a certain amount 

 on the vertical plates, they dropped off from their 

 own weight, and fell to the bottom, where the trans- 

 verse plates retained them. Experiments were made 

 as to the distance from the works at which the de- 

 posits were made ; and at a short distance away was 

 found nearly all the mechanical dust, that from vola- 

 tilization being a little farther on. There was no 

 material diminution in the draught occasioned by the 

 introduction of the plates. The dust collected so 

 quickly and to such an extent that it became a serious 

 question as to how to remove it. The flues were con- 

 structed with manholes at the top, and the dust was 

 in such fine state that the men would be subjected to 

 the danger of suffocation. The problem was solved 

 by setting fire to the flue and burning the dust, which 

 was found in agglomerations easy to remove, and in 

 just the condition to be put into the furnace. The 

 removal was a matter of little difficulty, the manholes 

 having been changed to the sides of the flue. Next 

 arose the question of temperature, and whether or 

 not the lowering of it had any effect on the collection 

 of the dust. It varied from 300° C. near the chim- 

 ney to 64° C. at some distance from it; and it was 

 found that the degree of heat made little difference. 

 This led to important conclusions ; and the substitu- 

 tion was begun, near the chimney, of pasteboard for 

 the iron jilates. They answered the jjurpose just as 

 well, provided they were of sufficient thickness to 

 sustain themselves, and were also much cheaper. 

 After the success of these experiments, the method 

 of cleansing flues by water will probably be aban- 

 doned. They have demonstrated the importance of 

 surface over volume, and of the rectangular against 

 the arched flue. It is doubtful if any method can 

 save the whole of the material carried off by mechani- 

 cal means or volatilization ; but it is proved that there 

 can be saved two or three times more than was be- 

 lieved possible. 



President Eothwell said that he had visited these 

 works, and had taken much interest in going over 

 them. By the process, a saving of about four per 

 cent is effected over the old way; and Freidenbach 

 charges a royalty of two per cent, or one-half of what 

 he saves. Since the collection of the dust by burning, 

 the pasteboard surfaces had been dispensed with, as 

 they would be destroyed. He had closely observed 

 the iron plates, and found that they were little affect- 

 ed. The first plates used were those which had been 

 discarded from the screens, and had been lying about 

 the yard, being as likely to be acted upon as any; but 

 they showed no signs of deterioration. He had ob- 

 served the same effect of surface in the collection of 



arsenic dust in the works at Deloro, although at times 

 he had been obliged to use a fan to secure a draught 

 in long flues. The fan, however, needs frequent 

 cleaning. His observations in regard to the ability of 

 the iron to withstand action by the vapors led him to 

 believe that arsenical chambers might be constructed 

 of the same material with advantage. In regard to 

 the flues at Ems, he had the fault to find, that they 

 were built partly beneath the ground, and were apt 

 to become too warm. He was in favor of building 

 them above ground, and on arched supports, which 

 would give the additional advantage that they could 

 be opened without stopping the run. 



Lines of -wreakness in cylinders. 



BY PKOF. B. H. BIOHABDS OF BOSTON. 



It has long been known to boiler-makers and to 

 the users of cylindrical pipes of many kinds, that, 

 when a tube is exposed to internal fluid pressure, the 

 resolution of forces is such that the material of the 

 walls of the tube is exposed to twice the stress in 

 the direction tending to produce longitudinal rup- 

 ture, that it is in the direction to produce circum- 

 ferential fracture. By longitudinal fractiue is meant 

 the fracture by a rent parallel to the axis ; by circum- 

 ferential fracture, fracture by rents running round 

 the cylinder. In consequence of this, makers of 

 boilers always lay the fibre of their metal around 

 the boiler; and the same is true with the makers of 

 gun-barrels. I have never seen any good and simple 

 illustration of this law until I met it in blowing 

 glass. If a thin bubble of glass be blown out in a 

 spherical form, and then exploded, it will be found 

 that the j)articles tumble into totally irregular shapes, 

 showing no special direction in the molecular struc- 

 ture of the material. If, now, a bubble of glass be 

 blown out, and so manipulated that it will take a 

 cylindrical form, and then be exploded, it will drop 

 into ribbon-shaped pieces from end to end ; and the 

 only parts that will be found, to differ from this form 

 will be the two hemisi^herical ends, which will remain 

 whole, having a fringe of ribbons representing the 

 lines of fracture from the cyliniler. The main point 

 of difference between this experiment and the acci- 

 dental explosion of large boilers appears to be, that in 

 a boiler the shell goes at its weakest point, and once 

 the rent is started it tears the boiler to pieces without 

 much regularity of lines : while in the glass cylinder 

 the walls are so nearly of the same strength that it 

 can hardly be said to have a 'weakest point; when, 

 therefore, it gets to its limit of strength, and is on 

 the verge of exploding, there is no one place to ini- 

 tiate the explosion, and the glass explodes everywhere. 

 This it does as it should do, by tearing into innu- 

 merable ribbons parallel to the axis of the cylinder. 

 If P = the pressure, and D = the diameter of the 



PD 



cylinder, then — n- = stress tending to longitudinal 



P D 



rupture, and —j- = stress tending to circumferential 



rupture. 



Professor Richards illustrated his statements by 

 experiments with glass tubing and a blast, with the 

 most complete success. 



The shop-treatment of structural steels. 



BY MR. A. F. HILL, OF NEW YORK. 



The speaker urged the importance in the manufac- 

 turing-arts of a knowledge of the effects on iron and 

 steel of the various processes to which those metals 



