OTAGO CEMENT.

Otago Witness, Issue 878, 26 September 1868, Page 3

OTAGO CEMENT.

In Dr Hector's supplementary report on the Mining and Mineral Products of the colony, published as an Appendix to the Reports and Awards of the Jurors at the N.Z. Exhibition of 1865, may be found his analyses of 'the Moeraki . boulders, as materials for the manufachire of hydraulic cement. It is as follows :—: — HYDRAULIC CEMENTS. An examination was made of the Calcareous Septaria, or Cement Stones, which occur in the lower tertiary clays that crop out on the coast at Moeraki, in the Province of Otago, in order to discover whether they might be made available for the manufacture of hydraulic cement.

The same formation occurs in other parts of the colony, but it is best known at the above locality on account of the singular appearance which these boulders

present, and which attract the attention of all who travel along the beach, from their perfectly spherical form. They occur of all sizes up to 6 or 8 feet in diameter, and consist principally of a mixture of clay with carbonate of lime and iron.

Their consolidation in the substance of these clay beds must have' been effected by the eccentric shrinkage which took place when their elements entered into chemical combination to form a natural cement. This is indicated by the circumstance that the fissures by which the 'spheres are traversed widen towards the centres of the boulders, and are closed externally, and they are only partially filled by a subsequent deposit of crystallised carbonate of lime. The richest septaria are those of small size, but portions of even the largest Trill yield moderately useful cement. The following analysis is of a portion of one ■of the boulders, free from crystallised carbonate of lime : — ANALYSIS. Soluble silica '80 Alumina and iron, partly as carbonate B*7o Carbonate of lime 72 40 „ magnesia '30 Insoluble in acid (clay) 1780 100Character, very hard and compaofc ; colour, mottled grey ; sp. gr. 2 655 ; hygroacopio water, '60 per sent, at time of analysis. This analysis shows that this specimen is' capable of affording a moderately good hydraulic cement, the percentage of clay t~eing 17.80, and that of the soluble silica '80. These proportions would, however, be a little reduced, if the septaria were worked upon a large scale, from the quantity ofjcalc-sparpresentintheformof veins. As a guide to the comparative value of these septaria, the following extract from Tomlinson's Cyclopsadia, articles Mortar and Cement, is appended — "Limestone containing 10 to 15 per cent. of clay — poor — sets in 14 days. Limestone containing 15 to 25 per cent, of clay — rich— sets in 2 or 3 days." Generally, if a limestone contains less than ten, or more than thirty per cent, of clay, it will not; furnish a cement. The analysis being so far favorable, a portion of one of these septaria was treated for cement according to the system generally pursued, and the product, when moistened and worked, and finally immersed in water, set to a moderately coherent mass in three days — thus proving by a practical test that it possesses the qualities of a hydraulic cement. A second sample of these boulders, similar in external appearance, was also analysed, but its composition was considerably different, and when tested practically it failed to form a proper cement. The defect, as will be seen from the following analysis, arises from an excess of sandy matter : — ANALYSIS. Sand 35.00 Clay 6.60 Alumina, with sesqui-oxide of iron 7.60 Carbonate of lime 50.80 „ magnesia traces. 100. Character : colour yellowish, not nearly go hard and compact as the former one, and is considerably affected by water.

It is said that a coat of gum copal varnish applied to the sole 3of boots and shoes, and repeated as it dries, uatil the porea are filled and the surface shines like polished mahogany, will make the soles waterproof, and also cause them to last three times as long as ordinary soles. In Connecticut the oyster-beds are staked out to the different owners, by commissioner* elected by the people, under well defined laws of the State. Every man, woman, and child resident in the State, is entitled to select two acres of oyster ground, not previously appropriated, withm the waters of the State. M. Replovsky, deacon of the Russian church at Stuttgard, has presented to the Post-office of St. Petersburg a letter-box, organised in such a way that the person who deposits & letter in it receives a ticket showing the year, month, and day cf the act. A commission appointed to examiae the invention has found it perfectly practical and well suited for the object proposed.

Ozone. — This remarkable substance, discovered by Schcenbein. in 1840, has lately been the subject of numerous researches. It exercises a powerful action upon organio substances, and it is this which has recently called it into notice again. It has been shown by Dr. Scharr, of Berne, that oz mo, aswellasßubstances impregnated with it, will kill animalcules with certainty and rapidity ; and, as recent researches seem to place it beyond a doubt that most epidemics, and cholera among the number, are owiny to microsoaria, great hopes are entertained of its being possible to use ozone in hospitals as a disinfectant ; and, perhaps, to exteud its use still further. Aa might have been foreseen, however, from its being a modification of oxygen, it exercises an irritating action on the respiratory organs, a drawback which must necessarily reduce its application to sanitary purposes within narrow limits.