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[May 9,1862. 220 THE PHOTOGRAPHIC NEWS. we shall succeed in accounting for, in a manner as as Fig. 18. Fig. 17. । snail succeed in accounting for, in a manner as precise circumstances permit, the changes which take place in the composition of a collodion prepared with acid pyroxi- line, either on account of insufficient washing, or on account of the decomposition it undergoes, in certain cases even after its solution. fault without remedy. Such an accident has not happened to me since the early days of collodion photography, whel the proper way of making the various instruments was Thus, a simple collodion to which wo have added iodine, with the intention of changing the latter into an iodide by means of slips of metal, becomes altered in the course of a few months, so that it disengages nitrous fumes, and mani fests a very acid reaction, and the sides of the bottle become covered with a quantity of small red crystals. Having had occasion to observe the simultaneous changes produced by time in alcoholic and ethereal solutions of iodine and nitric acid, we have only been able to refer the cause of this singular effect to the decomposition of the pyroxyline, the only body which can furnish the oxygen elements of the nitrogen. However, we have never observed similar results in nitric cotton; but the facts which Mr. Hardwich recently pub lished on the decomposition of this body, confirm us in our first supposition. (To be continued.) at all decided by experience, and unsuitable cement wasofte used for this purpose, but now I think they may generally be relied on. Still it would, no doubt, be better to incres the security by the addition of a silver rivet such as o employed to repair broken china, &c., which would render • disaster of this nature impossible except in the case “ breakage. It would be well if this kind of dipper were made ’ little wider than is usual, that the plates may have a mo? substantial support, and also the lip is seldom made 01 sufficiently thick glass to form a deep groove in which t I bottom edge of the plate can lie securely, so that it can od rest on the lip, and a little cause is sufficient to make it % off. Want of a proper attention to this detail is the princit cause of the glasses getting off the dipper in the bath, wh necessitates one of the most disagreeable kinds of fisbi" that I am acquainted with ; if the dipper be properly m in this respect, and the bath slightly inclined from t perpendicular, as mentioned above, no fear need ever • entertained of such a misfortune. If from the flatness of the surfaces the dipper is fo ol “ to adhere inconveniently to the inside of the bath or to t, back of the plate, one large drop of cement upon each S of it will remedy this entirely, as it will prevent the dipP" from lying perfectly flat against either of the surfaces. Another objection to glass dippers has been made, t they are apt to break the bath by striking with violela ; against the bottom. I do not think any remark is necesiin ’ on this point, except to recommend more careful manipulat C I to those photographers to whom such an event has occu! ' as it can only be the result of a want of ordinary attentiola Porcelain dippers are, in my opinion, preferable to thae constructed of plate glass, as last described ; they are all in one piece, therefore the lip can never give way "n by breaking, and it can be made of a more convenient foa When of the same thickness they are, I think, equally stro W and equally cleanly. It would be an advantage if they " made wider than is usual, especially those intended for 4 sized plates. Another improvement would be to make corrugated, or slightly grooved on both sides nearly to top ; this would add to their strength and also preven REMARKS UPON SOME OF THE APPARATUS EMPLOYED IN PHOTOGRAPHY* BY F. R. WINDOW. Baths and DrPERS (continued). Dippers fon Vertical Baths.—Dippers are so essentially part of thejvertical baths they are exclusively used with, that I will first say a few words respecting them before turning to the subject of horizontal baths. It seems to be generally admitted that the question of dippers is rather a sore point, and on turning over the leaves of this journal or other publications devoted to photography, we see frequently repeated complaints of the caprices and misdemeanors of these instruments, as well as many sug gestions of devices to correct their shortcomings. I am rather inclined to think, however, that they scarcely deserve all the ill that has been said of them, and that many mischances have been laid at their door which could be more appro priately attributed to other sources, and oftener than not, I fancy, to the photographer himself. A dipper is intended to hold the glass plate when it is plunged into the vertical bath, and to draw it out again. It must clearly be of such a form that no part of it can touch the front of the plate upon which is spread the delicate collodion film. For this reason they are made like a flat hook, the plate being allowed to rest against the back and on the bottom only. Dippers are made of plate glass, glass rod, silver wire, porcelain, and gutta-percha. Plate glass dippers are probably more used than any of the others. They are formed by cementing a small slip of thick plate glass on to the bottom of another strip of plate glass of the same width a trifle longer than the depth of the bath. The small slip of glass forms the lip or hook upon which the plate rests: it should, therefore, be thicker than any of the plates that are likely to be used, and before being cemented on to the dipper, the edge of the lip should be ground on a stone so as to form an acute angle with the back piece, (fig. 17); this forms a groove which offers the plate a firm seat, and if the lip be formed of sufficiently thick glass there is no danger of the plate slipping off. The great vice of this kind of dipper- appears from the complaints of several photographers to be the tendency of the cemented lip to come off, and as this naturally always happens at critical moments when the plates are being placed in the bath or taken out, it would be sufficient to condemn the instrument entirely, if the charge were, well founded, or the * Continued from page 196.
