FEBRUARY 20, 1891.] THE PHOTOGRAPHIC NEWS. 139 Pig. 4 represents a soap film in the first stage of disruption, fig. 5 in the second stage of disruption, and fig. 6 in the third stage. The falling bullets are photographed in each case. The shots at the moment of touching the film had attained a velocity of about 8 feet per second; the velocity of contraction of each film was about 48 feet per second. The soap solution used, and which gives films of considerable durability, consisted of a solution of three per cent, oleate of soda and twenty-five per cent, glycerine. The iron wire rings supporting the films were coated with solid paraffin; the films arc more durable when supported by paraffin. THE BLOW-THROUGH LIME-LIGHT JET. Ten years ago the lime-light was used almost ex clusively by professional lecturers; but since oxygen gas has no longer to be made for the purpose, but is supplied compressed in bottles as a commercial com modity, the light is employed by many hundreds of amateur workers, either as a luminant for the optical lantern, or as a source of light by which to enlarge photographs. Hence the choice of a suitable jet—by means of which the two gases employed can be made to impinge upon the lime cylinder—becomes a matter of great importance to many. We propose to offer a few remarks upon the different kinds of jets available, and to point out the advantages or disadvantages pertaining to each. Lime-light apparatus has of late been so perfected that the question of danger in its use may be almost, if not quite, eliminated. Accidents—and sometimes bad accidents—used to happen ; but these were gene rally traceable to some malpractice in separating the oxygen gas from the compound with which it was associated, or to accidental admixture of hydrogen with oxygen in the bag or bags employed. We may now rely upon the gas supplied in cylinders being quite free from any such dangerous admixture, for the nozzles of the two bottles are furnished with right and left screw threads respectively, so that neither of them will fit the supply pipe of the compressing apparatus which is not intended for it. By this provision absolute immunity from this source of danger is secured. The substitution of cylinders for bags also obviates a number of minor risks, which it is not necessary to mention in detail. In the choice of a jet the operator must be guided by his requirements. If he wish to be able to enlarge photographs, with the ability to show a few pictures occasionally by means of the optical lantern, and if he be content with the use of a screen or sheet about twelve to fifteen feet square, the blow-through or safety jet will suffice for all his needs. There is now no reason why this form of jet should be distinguished by the word “safety”; but the term is an attractive one to the tyro, and no doubt induces many to adopt that form of burner in preference to others. But the blow-through jet has other recommendations of a far more tangible nature. One of the necessary gases is obtained by the simple expedient of fixing an india- rubber tube to the nearest gas burner, and leading it to the hydrogen side of the jet. A cylinder of oxygen supplies the other gas, and by no combination of accidents can the two gases mix until they reach the point of combustion at the lime cylinder. But in the choice of a blow-through jet some judg ment is required, for many different patterns are in the market, and one kind will give quite double the light of its fellow without more expenditure of gas. A slight difference in construction makes all the difference. The cheapest—and, perhaps, the least efficient—form is where the 0 and H tubes are quite separate, and where the former bends over towards the mouth of the