FRAGMENTS OF SCIENCE. 



857 



mound extends for about twelve feet outside 

 for the greater pait of the circuit, and here 

 most of the bone and flint implements have 

 been discovered. The largest article found in 

 the site was a very fine canoe, thirty-seven 

 feet long and forty inches beam, dug out of a 

 single oak tree, which lay in what has proved 

 to have been a dock. A curious ladder wa9 

 also found here, the rungs of which were cut 

 out of the solid wood, and which has some- 

 what the general appearance of a post of a 

 post-and-rail fence. The exploration of the 

 site is much interfered with by the rising of 

 the tide, which covers the crannog for a con- 

 siderable time every day. All the relics 

 found — consisting chiefly of objects of bone, 

 staghorn, jet, chert, and cannel coal, with 

 some querns, the canoe, ladder, etc. — have 

 been placed in the museum at Glasgow. 



Portland Cement. — The following facts 

 are taken from an address delivered before 

 the Franklin Institute by Mr. Robert W. 

 Lesley : " It was not until the end of the last 

 century that the true principles of hydraulic 

 cement were discovered by Smeaton, who, in 

 the construction of the Eddystone Light- 

 house, made a number of experiments with 

 the English limestones, and laid down, as a 

 result, the principle that a limestone yielding 

 from fifteen to twenty-five per cent of resi- 

 due when dissolved in hydrochloric acid will 

 set under water. These limestones he de- 

 nominated hydraulic limestones, and from 

 the principle so laid down by him come the 

 two great definitions of what we now know 

 as cement, namely, the natural and artificial 

 cements of commerce. The natural variety, 

 such as the Rosendale, Lehigh, and Cumber- 

 land cements, was first made by Joseph Par- 

 ker in 1'796, who discovered what he called 

 1 Roman cement,' based upon the calcination 

 at low temperatures of the nodules found in 

 the septaria geological formation in England. 

 This was practically the first cement of com- 

 merce, and gave excellent results. Joseph 

 Aspdin, a bricklayer or plasterer, took out a 

 patent in England in 1824 on a high-grade arti- 

 ficial cement, and, at great personal depriva- 

 tion, succeeded in manufacturing it on a com- 

 mercial scale by combining English chalks 

 with clay from the river beds, drying the 

 mixed paste, and after calcining at high heat 

 the material thus produced, grinding it to pow- 



der. This cement, which was the first Port- 

 land cement in the market, obtained its name 

 from its resemblance when it became stone 

 to the celebrated Portland stone, one of the 

 leading building materials in England. The 

 rocks used in the manufacture of Portland 

 cement are very similar to those from which 

 natural cement is made. The various layers 

 in the natural rock may vary in size or strati- 

 fication, so that the lime, alumina, and silica 

 may not be in position to combine under 

 heat, or there may be too much of one in- 

 gredient, or not enough of the others in close 

 proximity to each other. In making Port- 

 land cement, these rocks, properly propor- 

 tioned, are accordingly ground to an impal- 

 pable powder, the natural rock being broken 

 down and the laminae distributed in many 

 small grains. This powder is then mixed 

 with water, and is made into a new stone 

 in the shape of the brick, or block, in 

 which all the small grains formerly com- 

 posing the laminae of the original rock 

 are distributed and brought into a close 

 mechanical juxtaposition to each other. 

 The new rock thus made is put into kilns 

 with layers of coke, and is then calcined at 

 temperatures from 1,600° to 1,800°. The 

 clinker, as it comes from the kiln, is then 

 crushed and ground to an impalpable pow- 

 der, which is the Portland cement of com- 

 merce. Portland cement may be made from 

 other materials, such as chalk and clay, lime- 

 stone and clay, cement rock and limestone, 

 and marls and clays. In every case the prin- 

 ciple is the same, the breaking down and the 

 redistributing of the materials so that the fine 

 particles may be in close mechanical union 

 when subjected to the heat of the kiln." 



The French Nontoxic Matches. — It is 



believed, by Frenchmen at least, that the 

 problem long sought, of finding a composition 

 for a match head in which all the advantages 

 of white phosphorus shall be preserved while 

 its deleterious qualities are eliminated or 

 greatly reduced, has been solved in the new 

 matches which the French Government has 

 placed upon the market. These matches are 

 marked S. C, by the initials of the inventors, 

 MM. Sevene and Cahen, are made in the fac- 

 tories at Trelaze, Begles, and Samtines, and 

 have been well received by the public. In pre- 

 paring the composition, the chlorate of pot- 



