2464 mg. per litre the density of the methyl bromide-air mixture is 8pPrOsiIIU3te~y 1.003 times that of air.The tests carried out during the airing periods were designed to &over how soon after the initial opening of the hold it would be mfe to unload the bags. It is generally agreed that a safe upper limit of concentration for exposure to hydrogen cyanide is 0.025 mg. per litrc (20 p.p.m.).? Continuous exposure to this concentration for several hours may produce slight symptoms. There is less agreement on the corresponding figure for methyl bromide. The maximum esfe concentration for prolonged exposure is variously stated, e.g., 100 p.p.m.8 and 50 p.p.m.@ Irish, Adams, Spencer and Rowem subjected various animals to daily exposures of about 8 hours for periorls up to 6 months and found that only rabbits were affected a t a concentration of 0.13 mg. per litre (31 p.p.m.) and these were unaffected at 0.065 mg. per litre (16 p.p.m.). In normal fumigation practice operators and workpeople will not be subjected to repeated exposures of such long duration. Special attention has been given to the determination of concentrations after a number of the bundles had been moved. In most cams about a dozen bundles were moved to form a deep hole in the centre of the covered portion of the hold. During normal unloading men would be working in the completely uncovered hold and would probably be exposed to smaller concentrations than have been measured in these tests. In such a test during Trial 2 with methyl bromide made 4) hours after the initial opening, a concentration of 0.05 mg. per litre was measured in a sample taken in a flask. A k s t with the Halide Lamp gaVC an estimated concentration of 0.15 mg. per litre. In a similar test hour after opening on the second &y of airing concentrations of 0.018,0-013 and 0.030 were measured. Similar results were obtained in Trial 1. The stacking of the bundles horizontally nppenrs to have had little effect on the rate of airing. It has been concluded that it would normnlly be permissible to unload the barge 24 hours after the initial opening provided that the hold had been open to the air for a t least 6 hours, and thnt the liatches had been completely removed for a t lenst 1 how before the commencement of unloading.An oxporimentnl investigation hae bwn mado into the offocta of a numbor of factors on tho msulta of siove ondyeis of natural ssnds. Tho factors studied includod samplo sizo, particlo size distribution in tho Bnmplo aiid tho duration of sioving. Microscopic oxamination showod that the particle shape was similar in all tho matorials toated mgardlom of size. Tho work showod that ovorloading of the siovos loads to inaccurate reaulta, md that mduction of Bnmplo size in a more effoctivo remedy for ororloading than prolongation of sioving time. Valuea are givon for tho maximum deairablo loading for n numbor of siovos, nnd mcommendetione am mado for tho adoption of a stnndord woight of sample far &yo analysis of natural mndn. Tho most rocent British Standard mothcd for Siovo Andysb ...

Summary The British Standard for concrete aggregates (B.S. 882:1944) distinguishes “rounded” from “angular” aggregates, but gives no method for defining or measuring different degrees of angularity. The present article describes the development of a test for this purpose. A study of the literature was followed by experimental work which showed thar the most suitable method for expressing the degree of angularity of gravels was the measurement of the proportion of voids in the single-sized aggregate when compacted in a prescribed way. This proportion was found to vary from about 33 per cent in a well-rounded beach gravel to about 45 per cent in a very angular crushed rock. The test result is expressed thus:— “Angularity number” = percentage voids — 33. The angularity number of about 100 samples of aggregate ranged from 0 for very rounded gravel to 11 for an angular crushed material, and showed good agreement with personal opinions of the relative angularity of the samples and with the compacting factor of concrete made from some of the aggregates. Full details of the method of test are given in an appendix.

The British Standard test for the apparent specific gravity and absorption of coarse aggregate (B.S. 812: 1951) has been found to give variable results. The present paper describes an investigation made to devise a test that would not suffer from this variability.The factors thought to affect the results of the test were studied, and it has been found that the following modifications to the standard procedure are desirable:I . The size of aggregate tested should preferably be $-k in.The rate of corrosion of cast iron by the action of sulphate-reducing bacteria is increased by the addition of ferrous iron alone or the combined addition of ferrous iron and yeast extract. The addition of yeast extract alone, however, has a retarding effect upon corrosion. The specific action of the added ferrous iron is discussed and the rates of corrosion in heterotrophic conditions are compared with those in autotrophic conditions.

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Fifty-five samples of British rocks of restricted petrological type, namely quartz-dolerite, were examined petrographically and by mechanical testing. No general correlation was found between mineral content or grain-size and test results. Considerable correlation exists, however, between the test values and geological occurrence; the specimens from the Whin Sill generally yield test results superior to those from Scottish Permo-Carboniferous sills, whereas samples from Scottish dykes of I'ermo-Carboniferous and Tertiary age respectively form intermediate groups.