710 TJie Architectural Review and American Builders' Journal. [May, enlarge, continuing to do so for about thirty minutes, when the oil is broken up and detached. The doctor truly remarks, that there is value attached to tli is simple test. Green rape oil breaks up more slowly than sperm, but, after sixty seconds, its pattern is different, the circles being large and beautifully defined. Purified rape oil becomes much larger, in the pattern circles, than green rape, in the same time. " Lucca olive oil " gives a large repre- sentation in one minute ; in two minutes an extraordinary development; and, in three minutes, a very large "likeness." What the doctor means, by the expres- sion " likeness," we really cannot divine, for he does not say of what it is a likeness. Green olive oil gives but a small pat- tern in one minute, and differs from the Lucca. Seal and Castor oils give forms, which are very small. Dr. Moffat remarks, that, in making these observations, it is necessary to attend to the size of the drop of oil, the height it falls, the force with which it does so, and the perfect purity of the cold water, as well as its stillness, at the time of dropping the oil on it. The experiments are conducted in the following manner : — " From a small dry burette, drawn out to a fine point, filed up to a certain mark with the oil, cautiously let fall a single drop, at four inches height, upon the centre of the water contained in a common soup- plate, or glass basin. We shall assume that Lucca olive is taken. The drop should, at once, spread circularly, about four inches, on the water. If it does not do so at once, then the plate, or the water, is not clean ; and the water is to be poured out, the plate be well washed, and again filled. All rubbing with towels is to be avoided. At thirty seconds, the appearance of the repre- sentation is very lovely, having all the similitude of crochet work." This beautiful mode of producing patterns, of exquisite beauty, owes its origin to Charles Tomlinson, an English- man ; inventor of what are called Cohesion Figures, which are produced, as we have seen, by the forms assumed by various oils, dropped on water. These, though so admirable, were prac- tically useless, until Dr. Moffat discov- ered the method of transferring them to paper, with all their brightness of color, in perfect permanency. It is but to lay a piece of glazed surface paper on the pattern, for a moment ; remove and wash off the excess of ink, with water ; and your pattern is there, complete. The marbling of paper used by book- binders is produced by the dropping of indiscriminate blotches of pigment, of various colors, on water ; and taking them up, on paper. This operation, however productive of brilliant effects, is coarse, in comparison with that we now call attention to, which no doubt, in the hands of our ingenious artists and artisans, will confer very desirable ad- vantages on the ornamental department of Architecture. 0. — Mica is abundant in the United States. In some parts of Siberia it is still copiously quarried in large plates, and is emplo3 - ed as a substitute for window glass. It is also used for panes in the cabin-sashes of Russian and other men-of-war ; being perfectly exempt from breaking, through the concussion of broadsides. Concrete — The use of this composi- tion is coming more into notice than ever ; and the study of it cannot be too closely attended to. The reason of walls not being built of it oftener is the want of a perfect knowledge of the mode of making and putting it into moulds, in an economical manner, at the same time ensuring its greatest amount of hardness.
