284 



POPULAR SCIENCE MONTHLY. 



this into the central coil, which is sur- 

 rounded 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 ori- 

 fice can be regulated by means of an ebonite 

 rod, which passes up the axis of the appa- 

 ratus, 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 com- 

 pressed gas is passing to the point of expan- 

 sion, and so makes this gas, still under pres- 

 sure, cooler than it was itself while under com- 

 pression. 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 com- 

 pressed gas, and so makes the latter cooler 

 than before expansion, and also cooler than 

 ever after expansion. This intensification 

 of cooling (always assuming sufiicient pro- 

 tection against access of heat from the out- 

 side) 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 centknetres in four 

 minutes. 



How Opinm is Prepared. — The English 

 consul at Ispahan gives the following de- 

 scription of the process : The people com- 

 mence 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 work- 

 man 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 Metliod of Identifica- 

 tion. — In a recent letter to Nature, Kuma- 

 gusu 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, some- 

 where about 650 a. d. He has found a pas- 

 sage in the Arabian Relation des Voyages 

 by one Sulaiman, who made several voyages 

 to China and India in the middle of the 

 ninth century a. d. (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 re- 

 spect 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 bor- 

 rower 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 de- 

 stroyed, they say to the borrower who denies 

 his debt : ' Declare in writing that that debt 



