Page:Popular Science Monthly Volume 49.djvu/298

284 this into the central coil, which is surrounded by a cylindrical glass vacuum-jacketed vessel as devised by Prof. Dewar. The two outer coils are separated from each other by vertical divisions of the case, and the spiral of the central coil is followed by a flat spiral of sheet copper. When the gas reaches the extremity of the central coil, it escapes through a fine orifice of peculiar construction, formed by bringing two knife edges closely together. The size of the orifice can be regulated by means of an ebonite rod, which passes up the axis of the apparatus, and terminates in a handle at the top. After its escape the whole of the gas cooled by expansion passes through the spaces surrounding the pipe in which the compressed gas is passing to the point of expansion, and so makes this gas, still under pressure, cooler than it was itself while under compression. The compressed gas consequently becomes, at the point of expansion, cooler than that which preceded it, and in its turn follows backward the course of the still compressed gas, and so makes the latter cooler than before expansion, and also cooler than ever after expansion. This intensification of cooling (always assuming sufficient protection against access of heat from the outside) is only limited by the liquefaction of the gas, the temperature of liquefaction being in the case of oxygen 180° C. The apparatus exhibited measures twenty-eight inches deep by seven inches in diameter, and when once cooled down—that is, in about half an hour—it yields liquid oxygen at the rate of about seven cubic centimetres in four minutes.

How Opium is Prepared.—The English consul at Ispahan gives the following description of the process: The people commence to collect the drug early in May. The poppy head is lanced in the afternoon, and the opium which exudes and dries during the night is collected into copper pots early the following morning. It is kept in store in these pots until required for exportation. Then it is taken out of the pots and sorted. For the succeeding manipulations, each workman has a smooth board, about twenty-three inches long and eleven inches broad. He takes from the bulk about one pound of the crude opium, and rubs it on the board for a short time, then puts it in the sun for ten minutes, and afterward takes it into the shade and rubs it continuously with an iron implement something like a small solid spade, until it dries up to a certain degree. It is then collected into a mass and heated in trays over a small charcoal fire until plastic. Each man then takes about a quarter of a pound, and kneads it again on the board until it dries up to the standard degree and assumes a golden yellow color. It is next made up into cakes of one pound each, which are wrapped up in paper and placed in tin boxes, in layers alternating with poppy chaff. These tin boxes are packed in wooden ones covered with hide and gunny, and the opium is then ready for exportation.

The Finger-print Method of Identification.—In a recent letter to Nature, Kumagusu Minakata gives some interesting data, which seem to indicate that the ancient Japanese use of finger marks on divorce papers, as a means of identification, which the author described several years ago in the same periodical, was probably adopted from the Chinese Laws of Yung-Hwui, somewhere about 650 He has found a passage in the Arabian Relation des Voyages by one Sulaiman, who made several voyages to China and India in the middle of the ninth century  (the time in which the above-mentioned dynasty in China was going to decline), describing the Chinese method of drawing up a contract: "The Chinese respect justice in their transactions and in judicial acts. If a man lends a sum of money to some one, he puts it down in writing. The borrower, in his turn, makes a similar writing, which he marks with two of his fingers together, the index and the middle finger. The two papers are put together and folded. Some characters are written across the portion where they join. They are then unfolded, and the writing by which the borrower acknowledges his debt is given to the lender. If, at a later time, the borrower denies his debt, he is told to bring the writing of the lender. If he pretends not to have it, and says he has never written a paper accompanied by his signature and his mark, and that his writing has been destroyed, they say to the borrower who denies his debt: 'Declare in writing that that debt