The Optical Magic Lantern Journal (July 1895)

The Optical Magic Lantern Journal and Photographic Enlarger. 115 another matter upon which the efficiency of a blow-through, or for the matter of that, any and every kind of limelight jet depends, and that is, the quality of the oxygen used. No amount of skill or experience can possibly ‘remedy the defects which occur when one has to work with impure gas. Where the gas is bad the results must be bad, no matter what quality of apparatus is used. It is only fair to say that the gas supplied commercially is generally of good quality and sometimes even excellent, but, on the other hand, I can remember occasions upon which the oxygen thus supplied has been obviously at fault. If you are aiming at superlative excellence of results I recommend you to make your own gas from the purest materials, but at the same time I may add my opinion that, in nine cases out of ten, you will have little to complain of if you use the ordinary oxygen procured from the dealers. If -you are satisfied that the oxygen you habitually use is all it should be, what about your limes? Long ago, when limelight was in its infancy, someone suggested the use of soft limes for blow-through jets. If you care for an expression of personal opinion in the matter, let me tell you that soft limes are of no advantage whatever, and that the use of them, moreover, is attended by several undeniable disadvantages. They are frequently ill-shapen, lop-sided things, they crack, often enough, for no reason at all, their keeping qualities are poor, they are too big in diameter and encourage the production of a large luminous surface instead of a brilliant point, and above all, they are at any time incapable of giving a better light than the smaller truly-turned hard lime. It will be wise therefore to see that your limes are not partially accountable for your failures. There is yet another point which the inexperienced lanternist is apt to disregard, and that is the opaqueness of the screen he uses. It too often happens that a blow-through jet is regarded ag a sort of second-rate piece of apparatus for which any makeshift in the way of a screen is suitable. Of course the very opposite of this is true; for the less the illuminating power of the system used, the greater the need of a really opaque screen. Those now sold by the dealers are most excellent, and I can strongly recommend their use whenever possible. One last word with regard to the blow-through jet, and that is, do not believe that it is so very much inferior to a mixed jet. Properly designed, well-made, and used with short focus lenses and other suitable accessories, it is capable of giving results very little inferior to those produced by the other forms. If it has a weak point, it is failure to give the best definition, but in this regard a bulky soft lime with its extensive luminous surface is often more to blame than the jet itself. . The satisfactory performance of a mixed jet depends upon much the same causes as the other, but in addition to these the question for the most suitable bore for the nipple has to be considered. ‘This again depends upon the pressure habitually used. If your gas is supplied from cylinders, where pressure is unlimited, the best light is obtained by the use of a nipple with a moderately large bore, but unless you always have sufficient pressure at your command I advise you to content yourself with the light obtainable from a nipple of medium size. Of course you read Tae Maaic Lantern JourNAL, well, when the next number comes to hand take a look at the letter ‘‘o’’ in the word ‘* post free” on the front page, the size of that letter will give you an idea of what I mean by a medium aperture for a nipple; the same letter in the word ‘‘ stationers”’ above it is too small, while the ‘‘o” in ‘Vol. 6” is largish, but perhaps not too large for an expert to use. If you are satisfied that the nipple of your jet is a suitable size and is not to blame for the poorness of light of which you complain, possibly the fault. may be sought for in the quality of the hydrogen you are using. You are probably well aware that under ordinary circumstances coal-gas and not pure hydrogen is supplied. The former is practically a3 good as the latter, except in one particular, and that is, its keeping qualities when stored for any length of time under great pressure, are uncertain. It may keep good for weeks, but on the other hand it may deteriorate in a couple of days to such an extent as to be almost useless for limelight purposes. Perhaps, therefore, the reason of your partial failure is to be found in the fact that you have been using coal-gas which has been ‘‘ too long in bottle.” One more caution concerning the practice with the mixed jet. The best results are only obtainable after considerable experience, and if this has been your first season with it you must not complain if occasionally the light has not been all you expected. Mixed jets vary much, and when you become more familiar with the peculiarities and requirements of the particular one you possess you will find your difficulties vanish. Lastly, there remains the growing family of saturators. If you have fitted your lantern with one of the well-known patterns but yet fail to get good results, I can only recommend you to apply to the makers or patentee, and so