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Crookes, O.M, FR.S.] (WITH WHich is incorporaTED THE "CHEMICAL GAZETTE"). 61 Ancient and Modern Mortar, by W. J. Dibdin 69 A B C FIVE - FIGURE LOGARITHMS CHEMISTS By C. J. WOODWARD, B.Sc. Logarithms of Numbers with Thumb Lateral Index-Instructions for CAPPER PASS & SON, LIM., BRISTOL, Weights of 1917. are buyers of LONDON: SCIENTIFIC BOOKS AND SERIALS. JOHN WHELDON & CO. have the largest stock in the country of LIBRARIES or SMALL PARCELS PURCHASED. SPECIAL CATALOGUES-Chemical, Botanical, Zoological, A. BOAKE, ROBERTS, & CO. (LIMITED), JOHN J. CRIFFIN & SONS, LTD., Stratford, London, E. KINGSWAY, LONDON W.C ANALYTICAL CHEMIST required by large firm A manufacturing Organic Chemicals. Must be a first-class Analyst, familiar with Commercial Methods, and have, in addition, a good knowledge of Organic Chemistry (preferably graduate). man is required who can devise new and standardise old methods of Analysis.-Reply, giving full particulars, in confidence, to Box 1/4, CHEMICAL NEWS Office, 16, Newcastle Street, Farringdon Street, London, E.C. 4. ENGINEERING TRADES (NEW INDUSTRIES) COMMITTEE. FIR IRMS or persons who will be interested after the War in manufacturing Scientific or Precision Apparatus of the following or analogous kinds, which hitherto have not been made in this country in quantities commensurate with the probable after-the war-demand, are requested to communicate with the SECRETARY of the above Committee at Armament Buildings, Whitehall Place, London, S. W. It is proposed to summon conferences, at early dates, of the several trades concerned to discuss the steps which should be taken to further the establishment or development of these industries. Correspondents should specify clearly the kind or kinds of apparatus which they propose to manufacture. LIST OF MANUFACTURES. Balances (Chemical and Precision); Barometers; Thermo neters; Hydrometers; Photographic Apparatus ; Cinematograph Apparatus; Clocks and Watches; Automatic Measuring and Registering Devices, with Clockwork Speed Indicators; Gauges (Pressure and Vacuum); Dividing Engines; Drawing, Mathematical, and Surveying Instruments; Screw and Precision Gauges; Measuring Machines; Micrometers; Spherometers; Microscopes; Field Glasses; Marine Glasses; Opera Glasses; Telescopes; Polariscopes; Spectroscopes; Spectrometers; Refractometers; Optical Apparatus generally; Lenses; Spectacle Lenses; Prisms; Physical Apparatus; Pyrometers, Feb. 8, 1918 aggregate to I volume of lime varied from 0'4 to 3'7, but in only four instances out of twenty-six was it more than 2, the average of these being about 1, as compared with the modern practice of 3. The best results of a large number of mortars prepared for experimental purposes and kept two years before being tested for crushing and tensile strengths, showed, out of 15 samples, that II contained 20 to 2.5 of aggregate to 1 of lime. Unfortunately, tests with 1 to I were not made. It will, therefore, be seen that in the matter of relative volume the ancient mortars contained larger quantities of lime than is considered permissible in modern practice. Nature of the Aggregate.-Modern specifications of the aggregate to be used for mortar generally state that this is to be "clean, washed sand, &c." On turning to the results of the analyses of ancient mortars of the twelfth and thirteenth centuries, and that of the London Wall, we find that the proportion of aggregate was not only less, but its character was largely that of gravelly sand with clean ferruginous clay, the quantity of the clay varying up to as much as 19.5 per cent of the aggregate. thirteenth century, collected by Mr. W. D. Caroe, The samples of mortar from Allington Castle, early F.R.I.B.A., were particularly interesting. The relative THE comparison between ancient and modern mortars presents many points of interest, amongst which may be more particularly mentioned the quantity of lime used in proportion to aggregate, the character of the aggregate, and the presence of clay. The quantity of soluble silica in some mortars has been quoted as proof of the action of the lime on the flint in the aggregate, but as will be seen later on, this is entirely fallacious. The strength of certain old mortars has been quoted as if the users possessed methods the art of which has been lost, but there is no evidence that such is the case, as properly compounded modern mortars will within a reasonable time possess strength equal to the best old samples obtainable. The work carried out by the author for the Science Com-proportions of lime to sand, &c., in three samples were mittee of the Royal Institute of British Architects during I to 17, I to II, and I to 1'9, the observations of Mr. the years 1907-8-9-10, following a paper read by him before Caroe when sending them being respectively, "Very good that Institute in December, 1906, on "The Composition indeed," "Not so good as A, but fair," and "In fair conand Strength of Mortars," brought to light many points respectively 8.6, 3.66, and 40 per cent on the sand, dition." The percentage of clean ferruginous clay was which had hitherto been but vaguely dealt with. An important point is that relating to the quantity of which was fairly coarse, the proportions of coarse sand lime used. It appears a simple statement to say to "I to retained on a 4-inch mesh being 20, 22, and 12 per cent 3," i.e., one volume of lime to three of sand. In practice respectively. The crushing strength of the first of the this appears to have been read in different ways. In some three samples was as high as 144 lbs. per cubic inch, and instances the volume of lime is measured as dry unslaked that of the second 90 lbs. Two other samples from the lime as received from the kiln. In others the lime has been same building contained lime in the proportions of I to I first "dry-slaked," and the required quantity taken from and 1 to 13; clean red clay in the proportion of 4'5 and the powdery mass, which has a volume per unit weight of 57 per cent of the aggregate, respectively; the crushing unslaked lime greater than that originally. In some cases strength being 162 lbs. and 194 lbs. per cubic inch respecthe slaked lime is first made into a "putty," kept for a tively. time, and then measured in that condition. For instance, in one case I cub. ft. of unslaked lime, after slaking, equalled 1.53 cub. ft., and in another the cubic foot was increased to 1'77, whilst still greater variations have been observed. Hence all statements of proportions of lime to aggregate are generally given in terms of unslaked lime, and in stating the results of analyses of mortar the volume of lime is calculated from the percentage of pure CaO on the assumption that the original lime was comparable to a commercial lime containing 80 per cent CaO, and multiplying the weight so found by 2, co correct weight to volume. This is necessary an arbitrary rule, but it is the only one available, and serves for practical purposes in the absence of definite information. The variation in the qualities of various limes may be diagrammatically shown thus Dover, and a Roman villa at Darenth, contained clean Two samples of Roman mortar, viz., from the Pharos, lime and broken brick only; whilst another from Threlfall Castle, near Hythe, contained clean flint and pebbles for the aggregate. Thus we see that there was no systematic method in the preparation of these early mortars, evidently materials however, being given to clean ferruginous, clayey, gravelly most conveniently obtainable being employed, preference, sand when obtainable. As showing the character of some of the mortar used after the Fire of London a sample from Painters' Hall, Trinity Lane, is interesting. This was built by Sir Christopher Wren, who evidently had little time to look Searles-Wood, F.R.I.B.A., and was found to contain lime after details. The sample was collected by Mr. H. D. and grit in the proportion of 10 to 0'5. There can be little doubt that a good proportion of this lime was due to the use of old mortar. It was unequally mixed, and contained lumps of lime, some soft and some hard, the "sand and grit" consisting of broken red brick and organic debris, evidently old rubbish from the ruins of the Fire, the earthy matter," clay, &c., in the grit being no less than 15'4 per cent. In this case the crushing strength was 110 lbs. per cubic inch. 66 In comparison with these results we may now turn to the best results obtained with experimental samples of mortar made with known materials and in proportions of lime to aggregate varying from 1 to 2 up to 1 to 5, and tested after being kept for two years (Table I.). These results show distinctly the reason of the advantage gained by the early builders in fixing their ratio at about 1 to 2, and the use of a coarser aggregate, as we have seen. The modern rush after economy, by reducing the quantity of lime, is very largely responsible for the falling off in quality. From these results it will be seen that the use of clay when the proportion of matrix to aggregate is 1 to 3 is disadvantageous with white chalk lime and greystone lime, but with blue lias lime a marked improvement is obtained with the Standard sand. Under other conditions the use of clay is distinctly advantageous. For instance, greystone lime and Standard sand were used in varying proportions, and the blocks crushed at the end of one month, with the results given in Table III. TABLE III.-Crushing Strength in lbs. per cubic inch. Standard sand Without clay, 5 vols., lime 1 vol... + 2 per cent clay, 5 vols., lime I vol. +5 per cent clay, 5 vols., lime 1 vol. +7 per cent clay, 5 vols., lime 1 vol. +10 per cent clay, 5 vols., lime I vol. + 10 per cent clay, 2 vols., lime 1 vol. Lewisham fine sand and natural clay 3 vols., lime I vol... Lewisham fine sand washed free from clay 3 vols., lime 1 vol. Voids in Aggregate.-An essential factor in regard to the strength of mortar is that relating to the voids, or empty spaces, between the particles. In the case of a mortar made with a sand having 40 per cent of voids the crushing strength was found to be only 70 lbs. per cubic inch, whilst with a sand having only 23 per cent of voids the crushing strength was 154 lbs. This explains why the proportion of lime, when used with coarse sand, should be in a greater ratio than I to 3, I to 2 giving far better results. The suggestion that soluble silicates are formed in the course of time is not borne out in the author's experience. As a test case, a mortar was made with pure lime and clean sand treated with hydrochloric acid and thoroughly washed. After twelve months it was carefully examined for soluble silica, when not a trace was present. The examination of numerous samples of ancient mortar revealed the presence of no more soluble silica than is normally found in ordinary fresh-made mortar. For instance, the mortar from the Roman Wall, London, contained only 0.30 per cent; those from Allington Wall, twelfth and thirteenth centuries, only 1.20, 0.70, 100, 0'42, 0.84, and o'68 respectively, and that from the Pharos, Dover, only 0.30 per cent. Certain cases are met with in which the soluble silica is much higher, as at Pembrey Castle, Caermarthen, thirteenth century, where the soluble silica was as much as 2.95 per cent, and the core of the old wall at Crosby Hall, where 3.8 per cent was found. Much higher results have been obtained, but in such instances the character of the mortar leads to the conclusion that trass or pozzuolan, &c., had been employed. fact that "on drying the mortar binds the stones between The setting of mortar was ascribed by Graham to the which it is interposed, and its own particles cohere so as to form a hard mass solely by the attraction of aggregation, for no chemical combination takes place between the lime and the sand, and the stones are simply united as two pieces of wood are by glue." "From the minute division of the silica and alumina in hydraulic mortar, their combination with lime is more likely to occur than in ordinary mortar. Still the fixing of the hydraulic mortar seems to be chiefly due to the fixation of the water and formation of a solid hydrate like gypsum." This view entirely agrees with my own experiments, as recited shortly in the foregoing, and I have no doubt that the process of crystallisation acts largely in connection with the "setting" of mortar and cement, assisted by aggregation. THE CONSTITUTION AND HYDRATION OF PORTLAND CEMENT.* By A. A. KLEIN (Worcester, Mass.). PORTLAND cement may be defined as the product produced by pulverising to a sufficient and definite fineness the clinker obtained by an incomplete fusion of a finely ground intimate mixture containing essentially lime, silica, and alumina in certain definite proportions. Iron, magnesium, sodium and potassium oxides are present almost universally in the product, although in the light of recent investigations indications are that these are not at all essential. Constitution of Portland Cement. The "whys and wherefores" of cements have been the subject of research and speculation for over one hundred years. Even before Joseph Aspdin took out a patent on the hydraulic lime he called Portland cement, Vicot in France had started his important investigations on the relation of the chemical composition of the stone used as a raw material to the quality of the product derived, on the nature of the constituents produced on burning, and on the chemical and physical reactions involved when limes and cements set and harden with water. Although some of his deductions were proved erroneous by later in * A contribution to a General Discussion on "The Setting of Cements and Plasters," held by the Faraday Society, January 14, 1918. |