1874.] Engineering. 125 
MM. Houzeau and Devédeix, composed of a combination of lime and 
aluminous lignites, which latter are found in abundance in the vicinity of 
Rheims. MM. Houzeau and Devédeix’s process was subjected to an extensive 
trial, and 2,500,000 cubic feet were thus treated in 1872. The cost for the 
purifying mixture per cubic foot was very trifling, and from the experience 
gained from the experiments, it was found that for treating the whole of the 
sewage waters of Rheims in this manner, the outlay would amount to £7000 
a year, besides the interest on capital expended; and the operation would 
produce about 33,000 tons of manure of an inferior value. Although, then, 
this agent of MM. Houzeau and Devédeix purified the water well, but at a 
high cost, the process could be considered in certain special cases as a com- 
plement to irrigation; but taken alone, it was evidently too costly. Irrigation 
was next tried, and, in consequence of the results obtained, the Sanitary 
Commission has recommended the acquisition of about 450 acres of suitable 
land. The estimated cost of works, &c., is £40,000, and the annual cost of 
maintenance and working about £3800. 
Boilers.—At the recent Vienna Exhibition, M. J. C. C. Meyn exhibited two 
of his patent high pressure boilers. This boiler consists externally of two 
cylinders, of which the upper is the smaller. The furnace is half internal and 
half external, and requires but little building. There is no bridge to the grate, 
which communicates dire@tly through a short vertical flue with a central com- 
bustion-chamber. This chamber is traversed by 76 flattened vertical water- 
tubes, which form one of the principal features of the boiler. They are 
wrought-iron welded tubes, with horizontal channels across their sides. 
Through these tubes the water circulates from the lower part of the boiler, 
and between them the flame must pass. From the roof of the combustion- 
chamber a double ring of tubes leads up to the upper part of the lower shell, 
the upper cylindrical shell being of such a diameter that it stands inside these 
rings of tubes. This upper shell is enclosed in a smoke-box of the same 
diameter as the lower shell, and made of sheet iron. ‘The ordinary water-level 
is two-thirds up the height of the upper tubes, and the upper shell, therefore, 
serves as a steam dome of large capacity, and has apparently been really 
effettual in preventing priming. The steam is led away from the top of the 
boiler through a pipe which forms atriple ring round it in the smoke-box before 
it is allowed to escape. 
A paper on the ‘Strength of Boiler Shells’? has recently appeared in the 
columns of the “‘ Nautical Magazine,”’ in which it is stated that the Board of 
Trade Surveyors have all along recognised as a fundamental principle of their 
practice the following opinion, expressed by Sir William Fairbairn, in 1854, 
viz. :—‘* Steam boilers of every description should be constructed of sufficient 
strength to resist eight times the working pressure, and no boiler should be 
worked, under any circumstances whatever, unless provided with at least 
two—I prefer three—sufficiently capacious safety-valves.” It appears the 
“*Galloway’s rule”? is most common amongst these surveyors, the rationale of 
which is that in the absence of tests witnessed by an officer of the Board of 
Trade, the strength of iron is assumed to be 48,000 lbs. per square inch in 
plates and rivets ; this includes the effect of fri€tion at the joints, and supposes 
the holes to be drilled, the strain to be applied lengthwise to the plate, and 
the rivets to be Lowmoor, or equal to that in quality. When the rivets are 
subjected to double shear, or where the strain is applied crosswise to the plate, 
only 43,000 lbs. is allowed as the strength per square inch of the rivet, or of 
the plate respectively. The section of the shell is taken as the length of the 
boiler by the thickness of the plate; but pradtically, the length of the section 
will be greater than the length of the boiler on account of the doubling of the 
plates at the circumferential seams. When the double rivetting is zigzag, as 
it should always be in boiler shells, the section is increased about 7 per cent 
by this extra material. To give effet to this, the 48,000 lbs. was increased 
about 7 per cent, or to 51,520 lbs., or 23 tons. A great deal of very valuable 
information and calculations are given in this paper, relative to the proper 
strength of boiler shells, but space will not admit of our following out the 
subje& further at present. 
