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1 1 pound 5 ounces 5 pints The fourth, the sodic alum hypo, in which carbonate of 1 pound 10 ounces 5 pints Shake, let settle for an hour or so, decant or filter. pints The plates fixed in the acid sulphite hypo were all badly pound pints 1 4 5 Hypo Saturated solution of alum Water pound ounces fl. drs. Hypo ... Water ... The second was the sodic hypo bath : Hypo Sal. soda... Water ... ... ... ... The third, the alum hypo, in which alum is added to the first or plain bath, and after the subsidence of the milkiness resulting, decanted or filtered :— soda and alum are both additional— Hypo Sol. of carbonate of soda (sal. soda) 1'4 Water ... ... - found on ca * As to the effect ot free acid in the fixing bath, note subsequently. I quantity of error possible in the use of different plates or films, an 8 by 10 plate after exposure was divided into four 4 by 5’s, and each of these immersed at the same moment (the baths being all equal in quantity, and likewise strength of fixing salt) in its own fixing bath, and left therein (until each and all were apparently completely fixed) an equal period of time. Then on removal they were similarly washed. The same treatment was accorded to an 8 by 10 plate cut into 4 by o’s, and not having been exposed. The first bath was the plain bath of simply hypo and water ; strength:— affected with sulphuration, and to a less extent, yet very badly, those fixed in the sodic alum hypo. The alum hypo bath gave plates which, although affected, were not so to as great a degree, while the sodic hypo and plain hypo baths gave plates entirely unaffected. The sidphuration in the case of the acid sulphite and sodic alum baths was most readily seen on inspection ; yet all the plates from each and all of the baths were subjected to the printing test, as several not showing in the least faulty on examination by the eye, failed in this, their final ordeal. In the matter of rapidity, of which observation was like wise made, fixation (here reference being to merely the visible clearing of the entire plate ; practically, additional time being advisable) was accomplished by the plain hypo bath the quickest of all; by the sodic hypo somewhat slower; by the alum hypo still slower; by the sodic alum hypo slower yet; by the acid sulphite slowest of all, very tedious, and at times unaccomplishable.—Wilson's 1 Photographic Magazine. The fifth, the acid sulphite hypo : Hypo Soda bisulphite ... Acetic acid W ater pound 33 pints practice there is no special objection, many of our older and most experienced operators, both here and in England, adding it, or carbonate or water of ammonia, to neutralise any free acid often present.* That, by the addition of alum, hardening of the film is indeed effected, but, as seen at once, by such very hardening permeation is opposed, and fixation retarded, while, at the same time, from its chemical composition (K,SO,Al,(SO—24 H,O), weakening of the bath with manifest evolution of sulphur takes place. That, by the addition of an acid sulphite, still greater and more pronounced like results ensue. E. J. Wall, “ Dictionary of Photography,” says : — “ The addition of any acid to a solution of hyposulphite will cause evolution of sulphurous acid and deposition of sulphur. “ The alum should be omitted from the fixing bath, as it decomposes part of the hypo, and weakens the fixing powers, besides rendering sulphur deposition liable.” And such is the consensus of opinion of most photo graphic workers and scientists. To the foregoing it may be said that “ theory is all well enough,” but what are the facts? For it goes without question that an established fact outweighs the most elaborate theories, it matters not how many or erudite the authors. Theory, for the most part a mere explanation of observed facts, has here contrarywise been supported thereby ; the results of the trials being as follows. of simply hypo and water, we render the bath for a surety alkaline, without altering its nature otherwise. To this SLOW COMBUSTION OF GASEOUS MIXTURES. When moist electrolytic gas is heated at 305° in glass vessels over mercury for one to two weeks, combination takes place between the oxygen and hydrogen, and only a very small volume of gas remains ; in absence of mercury, combination takes place only very slowly at 3053, and at 448° the diminution of volume is very small, but at 518° a considerable quantity of water is produced. The thin glass bulbs provided with lateral capillary tubes, which were employed in most of these experiments, can be sealed without danger of explosion if a little air is permitted to enter the point of the capillary, but even traces of air or other impurities have such a great influence on the reaction that the results are very variable, and, consequently, the relation between the time and the amount of combination could not be determined. The temperature of explosion of electrolytic gas, and that of a mixture of oxygen and carbonic oxide in theoretical quanti ties, lies between 518° and 606° when thin sealed glass vessels are employed. A number of experiments were made in order to try and determine the rate of combination of oxygen and hydrogen In the consideration of these baths theoretically, we have : That, by the addition of carbonate of soda to that 1 1 5 under certain conditions. For this purpose electrolytic gas, generated by the electrolysis of hot water, and consequently free from ozone and hydrogen peroxide, was passed for many days through a series of bulbs fused together by means of very small capillary tubes. The apparatus was very carefully cleaned, the gas was dried with concentrated sulphuric acid, and india- rubber, cork, and all organic substances were carefully ex cluded ; in some of the experiments the bulbs were heated at a faintly dull-red heat, and the pure electrolytic gas passed for eight days. The bulbs were then sealed before a blowpipe, and heated in the vapour of sulphur or of phosphorous penta sulphide (b. p. 518°) under the same conditions. In spite of all precautions, the results of the experiments were very variable, and no relation between time and amount of com bination could be determined ; it would seem, therefore, that the glass surface, even when most carefully cleaned, has a modifying but variable action on the electrolytic gas, and that this action is sufficiently different, even in the case of two exactly similar bulbs, to cause great irregularities in the ex periments. Bulbs containing pure dry or moist electrolytic gas can be sealed without danger when the capillary tube is sufficiently fine (| to } mm. in internal and 4 mm. in external diameter) ; in the case of the moist gas, a small flame can be observed running along the capillary when the tube is being sealed, but it goes out before reaching the bulb ; no flame is seen in the case of the dry gas, the volume of which undergoes no appreciable diminution by combination taking place. The electrolytic gas employed in the above experiments was found on careful examination to be free from any appreciable - f air. — Journal of the Chemical Society.