178 



POPULAR SCIENCE J^EWS. 



[December, 1888. 



and as small a diaphragm used as is possible. 

 From the second negative thus produced, any 

 number of positives can be printed. 



OPTICAL ILLUSIONS. 

 Figs. 1 and 2 represent two figures with curved 

 sides. One would say at the first glance that 

 Fig. 2 is much the longest, but actual measurement 

 will show that they are of exactly the same size. 

 The illusion is due to the fact that Fig. 1 is really 



pushed considerably to the left, although, as the 

 left-hand ends of both, are nearly in the same 

 line, the displacement is not apparent. 



Fig. 3 is another similar illusion. The fine dots 

 on the lower line are exactly the same distance 

 apart; but the differently shaped triangles placed 

 above them so confuse the eye, that the distance 



Fig 3. 



between the dots at the ends and the adjoining 

 ones appears greater than between those in the 

 middle of the line. The old proverb is not quite 

 true; for " seeing " is not always " believing," as 

 the above diagrams show. 



LABORATORY NOTES. 



New Reagent for Salts of Copper. — A 

 solution of neutral sodium sulphite in which a little 

 pyrogallic acid is dissolved, gives an intense blood- 

 red solution in aqueous copper solutions of medium 

 concentration. 



Desiccation of Gases. — Dibbits has pre- 

 viously shown how much moisture remains 

 unabsorbed by calcium chloride at different 

 temperatures. Sulphuric acid leaves approxi- 

 mately i milligram of moisture in 100 liters of air 

 Morley finds that the proportion of moisture not 

 absorbed by phosphorous pentoxide is only i milli- 

 gram in 1,000 liters of gas. 



Cleaning Platinum Dishes. — Dr. P. Vieth 

 states that the loss in weight of platinum dishes is 

 due mainly to the methods of cleansing them. 

 Using a large number in milk analysis, he recom- 

 mends that they be treated with hot sodic carbon- 

 ate solution and kept heated for about a lialf-hour; 

 this is thrown away and the method repeated, 

 using a bass-brush (a soft fibre made from some 

 kind of a sedge), then hot water, arid wiping dry 

 with a duster. No substance should be used like 

 sand, emery, or similar material. 



Method for Generating Pure Non-arsen- 

 iFEROus Sulphuretted Hydrogen. — Clemens 

 Winckler takes 100 parts heavy spar, 25 parts of 

 coal-dust, and 20 parts of common salt.. The two 

 former ingredients are finely ground, the salt is 

 added, and the whole made up with a little water 

 into a ball, which is rammed into a crucible of 25 

 centimeters in height and 10 centimeters in widtli. 

 When dry, some coarse coal is laid above the mass, 

 the lid is put on, luted down, except a small vent- 

 hole, and heated for some hours to incipient white- 



ness. The heat is then allowed to go down, the 

 crucible taken out of the furnace and let cool 

 quickly. The barium sulphide must be preserved 

 in stoppered bottles in a dry place. With dilute 

 hydrochloric acid it yields a very regular current of 

 sulphuretted hydrogen, free from arsenic. 



Rapid Filtration. — Precipitates which clog 

 an ordinary filter may be drained and washed, even 

 without the aid of a filter pump, by means of a 

 simple expedient described by A. B. Clemence 

 (Journ. Anal. Cltem.). Cut off the apex of a filter, 

 folded in the ordinary manner, leaving an opening 

 one-eighth inch in diameter. Close this opening 

 with a wad of ab.sorbent cotton, pressed down wliile 

 wet, or drawn into its place by suction with the 

 mouth. The ash in a portion of the cotton may be 

 ascertained beforehand for fine quantitative work, 

 but this should be very small. 



A Glycerine Reaction. — A pharmacist at 

 Hatten, named Merkling, has disSovered what he 

 supposes to be a characteristic reaction for glycer- 

 ine. A borax pearl, he says, moistened with 

 glycerine or with a small quantity of glycerine 

 sohition, and then he;ited in the blowpipe flame, 

 colors the flame green. This reaction will, he 

 assures us, enable the operator to detect as little 

 as one per cent of glycerine in a watery solution. 



Paper for Cleaning Lenses. — Profe.ssor 

 Simon Gage of Cornell University strongly recom- 

 mends the Japanese paper napkins for wiping and 

 cleaning lenses. Professor Gage says, " I used, 

 prior to the Japanese paper, the ' silver tissue ' 

 used by jewellers for wrapping fine jewelry, silver- 

 ware, etc. Both papers are entirely free from kaolin 

 and other material likely to scratch orinjure lenses ; 

 and as they can be had at ' next to nothing,' a fresh 

 piece can always be used, thus avoiding the dust of 

 the atmosphere which settles on every thing ex- 

 posed, even for a few minutes, in large cities." 



Improved Automatic Valve for Flasks — 

 A correspondent of tlie Chemical Neivs describes 

 a new form of valve for automatically sealing the 

 mouth of flasks, as follows: "Having often been 

 annoyed by the frequency with which the valve 

 made of india-rubber tubing — generally used when 

 performing analyses by reduction — gets out of 

 order, and will not act, I was led to make use of a 

 modification, the nature of which is explained in 

 a few words: Instead of the piece of tubing with a 

 slit in it, I make a glass bulb, the size of which 

 varies with that of the flask in use, and over this 

 bulb I slip a small piece of india-rubber tubing 

 suflicient to cover the bulb completely. The shank 

 of the bulb should be about three centimeters long, 

 and should be dropped into the neck of the flask, so 

 that the globular portion rests on the top. When 

 ebullition has entirely cea.sed, and the flame is 

 removed from under the flask, the partial vacuum 

 caused by the rapidly cooled gases inside draws 

 the bulb tightly down on the flask neck, thus 

 making a perfectly air-tight stopper, which requires 

 considerable force to remove." 



INDUSTRIAL MEMORANDA. 



Prepared Mortar. — In Berlin and other large 

 cities in Germany, mortar is manufactured in large 

 quantities, and sold to builders by the barrel. 



A Useful Magnet. — At the great steel-works 

 in Cleveland a large electro-magnet is used, sus- 

 pended from a crane, to pick up iron or steel bars 

 and billets. It will take up eight hundred pounds, 

 and, as soon as the electric current is turned off 

 after moving, drop it in the proper place, thus 

 doing tiie work of a gang of men. 



The Power of Niagara. — Professor Ayrton 

 has calculated that 1200,000,000 worth of force is 

 wasted annually at Niagara Falls, — wasted in the 



sense of not being used. He says, " If we take as 

 a low estimate that a large, well-made steam-engine 

 burns only 2 pounds of coal per horse-power per 

 hour, the coal consumption which would be equiva- 

 lent to the waste of power at Niagara would exceed 

 150,000,000 tons per annum, which, at only $1 25 

 or $1.50 per ton, means some 1200,000,000 wasted." 



The Compressed Carbonic-Acid Gas Indus- 

 try IN Germany, in consequence of the running- 

 out of the patent rights two years ago, is now worked 

 in ten factories, instead of in two, as formerly. The 

 Berlin Limited Company, the first of the kind, which 

 has also works on the Rhine, has an annual sale of 

 about 500,000 kilometers. Of the compressed gas, 

 about 70,000 kilometers are used in Berlin daily. 

 The price, with the increased competition, has 

 fallen from $4.00 for an 8-kilometer bottle, to $1.25. 



The English Fast Train Record. — During 

 the recent railway racing to Edinburgh and (jlas- 

 gow the North-eastern Company made no change 

 in their engines. The regular engines that liad 

 been on the Scotch service were used all the time, 

 and in nearly all ca.ses these were compound engines. 

 They had a pretty heavy train throughout, and well 

 filled with passengers and luggage. On the last 

 day of the accelerated running they ran into Edin- 

 burgh thirty-four minutes before time. The run 

 was done from Newcastle to Edinburgh, 125 miles, 

 in 128 minutes by compound engine No. 117. This 

 is at the rate of 58.6 miles for the whole run, and 

 beats the record. 



The Highest Chimney in the United States. 

 — The chimney which has just been completed for 

 the Clark Thread Company, at Newark, N.J., is the 

 highest chimney in the United States, and one of 

 the highest in the world. Three higher stacks are 

 cited as existing in Scotland, but they were built 

 for carrying off noxious fumes from chemical works, 

 and not for creating a draft for steam-boiler fur- 

 naces. These chimneys are Townsend's, at Port 

 Dundas, Gla,'gow, which is 454 feet high; Saint 

 llollox, at Glasgow, i'dQ^ feet high; and Dobson & 

 Barlow's, at Bolton, 367 feet high. The Clark 

 chimney is 335 feet high, and supplies draught for 

 32 boilers, having an aggregate capacity of 4,000- 

 horse power. The cost of the chimney is said to 

 have been $35,000. 



To Cool a Hot Journal. — Quite an ingenious 

 way of cooling a journal tliat cannot be stopped is 

 to hang a short endless belt on the shaft next to the 

 box, and let the lower part of it run in cold water. 

 The turning of the shaft carries the belt slowly 

 around, bringing fresh cold water continually in 

 contact witli the heated shaft, and without spilling 

 or spattering a drop of the water. 



Iodide of Mercury in Tanning. — The addi- 

 tion of a small quantity of iodide of mercury to 

 skins is found to effectually prevent fermentation 

 setting in, and at the same time to produce no 

 injurious effects in the subsequent tanning opera- 

 tions. It is said that the mercury salt acts as a pre- 

 servative of the constituents of the tannin liquors, 

 and that leather produced from skins that have 

 been previously treated in this manner is superior 

 to that tanned in the ordinary way. ^lessrs. Col- 

 lin & Benoist, the French chemists, who have ex- 

 perimented with this anti-ferment, state that it 

 completely prevents the liquefaction of the gelatine 

 which takes place in putrefying hides, and thus 

 saves them from this loss. A saving is also effected 

 by its use in the prevention of the decomposition 

 of the tannin in the tanning liquid, which is usu- 

 ally hastened by the introduction of the hides when 

 in a state of decomjiosition . The amount of iodide 

 of mercury required is so small, that there is no 

 possible danger from poisoning, either to the woik- 

 men or to those subsequently using the leather, in 

 its use. 



