SECTIONAL TRANSACTIONS.—G. 437 
and eddy formation. The ‘coefficient of friction’ of a mixture of air and 
water flowing through pipes was discussed. An experimental air-lift pump, 
dealing with acid mine liquors and delivering five hundred to six hundred 
gallons per minute in two lifts of about a hundred feet each, with a pump 
efficiency of 60 per cent., was described. The cause of pulsating flow in air-lift 
pumps was discussed, also the most efficient design of foot-piece for delivering 
air. 
18, Dr. Daviv Exurs.—Iron Bacteria in Relation to the Incrustation 
of Pipes. 
The connection between the activities of iron bacteria and the incrustation 
of pipes is so close in many cases that it is necessary to know the life histories 
and the physiology of these bacteria. The change that the deposition of iron 
causes in the appearance of some of the organisms is so great that identities are 
sometimes difficult to establish. The iron bacteria that are found in water 
reservoirs and give trouble to the water engineer are the following : Leptothriz 
ochracea (Kiitzing), Gallionella ferruginea (Ehrenberg), Crenothrix polyspora 
(Cohn), Cladothrix dichotoma (Cohn), Spirophyllum ferrugineum (Ellis). Iron 
bacteria must have organic matter to maintain life, so that the examination of 
organic matter in the water in which the pipes are immersed is of cardinal 
importance in solving troubles brought about by the incrustation of pipes. 
Trouble in the pipes may take one or more of the following forms: (1) Slimy 
streamers.—These owe their existence to the activities of iron bacteria and 
other similar organisms. The reproductive cells of bacteria fasten to the walls 
and are helped by slime from other micro-organisms. Organisms are usually 
Gallionella and Spirophyllum. (2) Tubercular incrustations.—Tubercles often 
form in the absence of organisms, but if present they exert an accelerating 
action on the formation of the tubercles. (3) Jron incrustations on non-ferru- 
ginous surfaces.—These result from the activities of iron bacteria with possible 
help from other organisms, as the walls are not corroded. (4) Spongy disease 
of iron.—The iron bacteria play no part. The remedy is to be found by ascer- 
taining in each case where iron bacteria, are concerned the amount of organic 
matter that is present in the water and then taking means to eliminate it by 
oxidation in some form or other. This can be done by direct oxidation or in- 
directly by the introduction of nitrifying organisms by a system of filtration. 
The acidity of the water must be reckoned and the mineral constituents of the 
water altered so as to be unsuitable for iron bacteria. 
19. Prof. C. E. Inecuis.—Two-dimensional Stresses in Rectangular 
Plates. 
20. Mr. J. D. Warson.—The Utilisation of Sewage Gas for Power 
Purposes. 
21, Prof. Trmosuenxo.—Impulsive Stresses in Rails and Girders. 
22. Prof. Titosuenxo.—The Vibration of Bridges. 
23. Prof. Henry Bricas.—Two New Forms of Rescue Apparatus for 
Use in Mines. 
The communication described two forms of rescue apparatus, namely, the im- 
proved Aerophor (liquid air) apparatus and the Briggs (compressed oxygen) 
apparatus. These appliances have been designed to comply with the more 
stringent requirements as to breathing apparatus in mines now stipulated by 
official regulations. The improved Aerophor has been evolved by the chief 
officers of the Newcastle and Mansfield groups of rescue stations and possesses 
improvements in the receptacle for holding the charge of liquid air, in the 
purifier for abstracting carbon dioxide from the air, and in the valves and in 
the general arrangement and construction of the appliance. The Briggs 
apparatus is described in full in the Second Report, Mine Rescue Apparatus 
Research Committee (Department of Scientific and Industrial Research), but 
since the latter report was written it has undergone further improvement. The 
