Mar. 23, iSSS.] 



SCIENTIFIC NEWS. 



'85 



President, in the chair, a paper was read on " The Effect 

 of Sea-water on Portland Cement," by Henry Faija, 

 M.Inst.C.E. 



The paper referred to the failure of certain concrete 

 work at Aberdeen Graving Dock, and the author first 

 alluded to the several published reports ascribing the 

 failure to the chemical action of the sea-water on the 

 cement. After pointing out that Portland cement has 

 been used in marine works for forty years, and that until 

 now any failures that may have occurred have never 

 been traced or ascribed to the chemical action of the sea 

 on the cement, the author gave a general description of 

 the work carried out at Aberdeen, embodying extracts 

 from the reports of Mr. Smith, Professor Brazier, and 

 Mr. Messent, descriptive of the manner in which the 

 cement was used, the specification to which it was sup- 

 plied, and the argument on which their theory is based 

 — which is, briefly, that the magnesia precipitated from 

 the sea-water enters into and becomes a compound part 

 of the cement, thus destroying it. The presence of mag- 

 nesia in cement was then considered, and the reason 

 explained why it is deleterious, when in excess, but the 

 magnesia as precipitated from the sea-water was shown 

 to be in a very different condition to magnesia when it is 

 incorporated in a cement in the course of manufacture. 

 The result of a large number of experiments, comparing 

 the behaviour of cement when gauged in sea-water and 

 when gauged in fresh water, the analyses of the cements 

 before and after gauging, and of the scale on the surface, 

 together with the scum and sediments in the waters in 

 which the cement had been placed, were given. 



The specification and the analysis of the cement used 

 at Aberdeen were then considered, and it was pointed 

 out that, though such a specification was not antagonistic 

 to the production of a good cement, there was nothing in 

 it which ensured a good and sound cement being de- 

 livered, and it was suggested that one or other of the 

 methods now known for determining the soundness of a 

 cement should in all cases be used, the author being of 

 opinion that, given that a cement is well ground, and is 

 proved sound, it will, in nearly all cases, be strong enough 

 for any purpose for which it is likely to be used. The 

 concrete at Aberdeen was used in what is called a 

 " plastic" form — i.e., it was allowed to partially set, and 

 was then broken up and placed in position. The danger 

 of using cement in this manner was shown, and the 

 results of several experiments given, proving that under 

 certain conditions the cement never resets. 



The conclusions arrived at were that sea-water has no 

 deleterious chemical action on a sound and properly used 

 Portland cement, and that the failures at Aberdeen must 

 be attributed to some other cause ; either to an inherently 

 bad cement having been used, or to the injudicious use of 

 it in a plastic form. 



Liquid Blacking.— A well-known liquid blacking is com- 

 posed in the following manner : — Very finely ground animal 

 charcoal, or bone black, is mixed with sperm oil till the two 

 are thoroughly commingled. Raw sugar or treacle mixed 

 with a small portion of vinegar, is then added to the mass. 

 Next, a small measure of dilute sulphuric acid is introduced, 

 which, by converting into sulphate a large proportion of the 

 lime contained in the animal charcoal, thickens the mixture 

 into the required pasty consistence. When all effervescence 

 has subsided, but while the compound is still warm, vinegar 

 is poured in until the mass is sufficiently thinned, it is 

 ready to be bottled for the market. 



CORRESPONDENCE. 



The Editor does not hold himself responsible for opinions expressed 

 by his correspondents, nor can he take notice of anonymous com- 

 munications. All letters must be accompanied by the name and 

 address of the writer, not necessirily for publication, but as a 

 guarantee of good faith. 



" A PECK OF MARCH DUST IS WORTH A KING'S 

 RANSOM." 



The true explanation of this old saying is lost sight of in the 

 Scientific News, March i6th, commencing with the query, 

 " Why should dry, windy weather be so valuable just now? " 



Some of the theories mentioned are, no doubt, correct, but 

 the main point is that, before barley and some other seeds 

 can be satisfactorily sown it is most important that, to en- 

 sure good results, the soil shall be in such a state of tilth 

 that a certain amount of dust can be seen to arise when it is 

 stirred by the harrows and drill. Spring corn, sown under 

 these conditions, germinates more regularly, and probably 

 means several sacks per acre more when harvested. 



This, calculated over a district, will amount to a sum 

 suflicient to ransom a king of the olden time, when the price 

 per sack was double what it is. The farmer now anxiously 

 looks for the appearance of the peck of dust. 



Alfred Taylor. 



MEAN VELOCITY OF THE WIND. 

 Your correspondent, J. Reginald Ashworth (Scientific 

 News, February 17th, p. 165) seems to doubt my statement 

 that "in our days smoke very rarely either rises or falls, but 

 is hurried along." My general impression is that the air is 

 sufficiently tranquil to admit of the smoke rising or falling 

 only during the brief "slack" which prevails when either the 

 polar or the equatorial current is dying away and about to give 

 place to its antagonist. But knowing the danger of trusting to 

 general impressions I have, since reading Mr. Ashworth's 

 letter on February i8tb, entered daily in my diary the cha- 

 racter of the wind. I find that out of the twenty-five days 

 included there have been only three days when the smoke 

 could be said to ascend perpendicularl)', and by day when it 

 was doubtful. My observations were made on a number of 

 chimneys in a northern suburb of London, including one 

 factory-chimney considerably higher than any of the surround- 

 ing houses. Cloud-Gazer. 



It seems to me that the behaviour of smoke as it leaves the 

 chimney may have been affected by other factors besides the 

 windiness or calmness of the weather. In the country ham- 

 lets, where the old weather proverbs were concocted, the 

 chimneys would be low and the houses very frequently 

 sheltered by trees. Hence there would be in those days 

 much greater possibility of the smoke issuing quietly and 

 rising or falling, as the case might be, than now they ar-e 

 much loftier, and the vicinity is laid bare of trees — the only 

 effectual screen against the wind. Thirdsman. 



INFLUENCE OF OCCUPATION ON HEREDITY. 

 The observations made by your correspondent "W" are 

 very interesting, and deserve to be repeated wherever there 

 is opportunity. Although 1 cannot give chapter and verse, I 

 fancy that I have met with similar or, at least, analogous 

 cases. Jerome. 



DO BIRDS AVOID POISONOUS FRUITS? 

 So says general opinion. On the other hand a popular and 

 somewhat sensational writer on natural history declares that 

 the berries of the arum are brilliantly coloured on purpose to 

 attract birds, which eat them and die, whilst their decomposing 

 remains furnish a rich manure for the seeds. But we cannot 

 find that he has ever met with a dead bird in the autumn, and 

 found the berries of the arum in its crop. On the other hand, 

 it is well known, that grain-eatirg birds may be destroyed 

 by poisoned seeds scattered in the fields. Hence it would 

 seem probable that birds become acquainted with the 

 poisonous fruits naturally growing in their country, but that 

 they have no mysterious faculty to warn them against 

 danger presentirg itself in some unknown form. Aruspex, 



