576 CURRENT TOPICS. [J. F. I.

red oil. Aqueous solut ions of t r i th iocarbonates are red, those of pe r th ioca rbona tes yel low in color. One molecule of t r i thiocar- bona te is able to combine with one a tom of sulphur to form one molecule of per th iocarbonate .

j . s. H.

Spontaneous Ignition of Fire Engine Hose While in Use . - - This phenomenon is described by A. H. GILL, of the Massachusetts Institute of Technology (Jour. Ind. and Eng. Chem., I92I , xiii, 168). The rubber hose was provided with two jackets of heavy cot ton fabric ; a new sectiola, 5o feet in length and 2 ~ inches in diameter , was used in a test ; cold r iver wa te r was pumped th rough it at the rate of app rox ima t e l y 25o gallons per minute. The vibration pro- duced in the hose by the pump, caused severe chafing of the cot ton jackets , and the reby genera ted grea t hea t ; finally the hose took fire be tween the cot ton j acke t s ; and both jackets were burned through on an area 2 inches long by I ~ inches wide. T h e same resul t was obta ined in several tests, us ing different types of fire engines and different makes of s tandard , h igh-grade hose. In some tes ts the cot ton jackets became charred in app rox ima te ly fifteen minutes.

J. s. H.

On the Closure of Small Cavities in Rocks Exposed to High Pressures. J. JOLY. (Phil. Mag., December, I92O. ) - -The speci- mens of rock examined were in the fo rm of spheres composed of two hemispheres wi th a com m on plane surface. In one of these a small hemispher ica l cavi ty was centra l ly ground, or a cavi ty was provided by laying a steel washer be tween the two hemis- pheres. The pressure was got by us ing a hydraul ic press. The t empe ra tu r e was tha t of the room and some of the tests lasted for months . I t was clearly shown " tha t in th i r ty tons on the plunger , that is, 38.7 o tons or 88,717 pounds per square inch, we have a pres- sure which is cer ta inly sufficient to close cavi t ies in grani te , basalt , obsidian, or l imestone."

G. F. S.

Fat Content of B u t t e r . - - T h e technic of the Babcock test for the de te rmina t ion of the fat content of milk or c ream has been modified by NELSO~ W. HEPBURN (Cornell University Agricultural Experiment Station Memoir 37, 663-69o (192o)) so tha t this test m a y be used for the de te rmina t ion of the fat content of but ter .

J. S. H.

A Series of Flights Made with a Free Helicopter. E. OEH- M I C H E N . (Comptes ]~endus, February I4, I 9 2 I . ) - - T h e helicopter had two propellers of diameter 6. 4 metres, which revolved in opposite directions. A stabilizing balloon containing hydrogen was rigidly attached to the chassis of wood. This sustained about 20 per cent. of

April, 192I.] CUP, RENT TOPICS. 577

the total weight of 336 kg., leaving 255 kg. to be lifted by the screws which were driven by a 25-horsepower motor of old type. In the month of January, I92I , 5~r. Oehmichen made several flights on board this aircraft. He went up only to a height of 3 metres above the ground, having a certain distrust of parts of the apparatus, and carry- mg no parachute. He reports an absence of pitching in the vertical plane containing the axes of the two screws, while there was consid- erable rolling. There was a remarkable stability in altitude. Land- ings without rebound were made when there was no wind.

The author lays stress on the profile of the screws which he planned to resemble the outlines of the wings of moths observed in motion by a stroboscopic method.

The fast series of flights were made in the presence of an officer formalh- designated to be a witness.

G. F. S.

The Problem of Soaring Flight. E. H. HANKIN, Chemical Ex- aminer to Government, Agra, India. (Proc. Cambridge Phil. Sot.. Michaehnas Term, I92O.)--Two kinds of soaring flight are shown 1)v birds, flying-fishes and dragon-flies. In slow flight speeds of from I I to 22 miles per hour prevail, while in rapid flight the speeds range from 33 miles per hour in the case of dragon-flies to 45 miles per hour for vultures. In the slow soaring flight of birds and fishes the tips of the wings are at a higher level than the body, while they are either flat or below the body in rapid soaring flight. As a rule, sun- shine must be present for slow soaring flight to be possible, while wind is indispensable for rapid soaring flight.

F. Handley Page remarks: " Doctor Hankin's discovery of the soaring flight of dragon-flies and flying-fishes affords a means of more closely investigating the phenomena of soaring. Observation of birds soaring at 2ooo or 3ooo feet is difficult compared with the observation of insect flight at a few yards' distance."

Cranes in a flock while in soaring flight keep their relative dis- tances with great exactitude. " They resemble a number of dead birds pinned on a blue wall." This " furnishes a clear proof that the energy involved does not come from any chance or irregular cur- rents of air." There remain two possible causes of such regular flight, c@., unobserved wing motions or some condition that is uni- form throllgh wide stretches of the air. Both dragon-flies and fishes retard their flight by adjusting parts of their bodies so as to act as brakes. This seems to rule out undiscovered wing motions as the cause, for, were flight due to such motions, it would appear probable that the speed of flight would be regulated by change in the wing motion and not by a braking adjustment. Moreover, an albatross cannot soar in calm weather near sea level. This it staould be able to do, were its soaring dependent on imperceptible wing motions.

l~ateral gusts of wind are not the cause of soaring as is shown by the position of the wings which is such that in some cases the thrust

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