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May 7, 1869.] THE PHOTOGRAPHIC NEWS. The words balance (French), bilanx (Latin), literally con strued, mean the double dish. A pair of scales for weighing substances consists of a beam or lever suspended exactly in the centre, having a dish or scale suspended at each end of it of exactly equal weights. The beam acts in a horizontal position, and is capable of turning upon its centre of motion. The extremities of the beam are called the centres of suspen sion. From these arc suspended the’scales, directly over the centre of motion; and midway between the centres of suspension rises a slender perpendicular' stem, upon the upper surface of the beam; this is called the tongue, and which, when the beam is horizontal, points to the top of the handle by which the whole is suspended. In a properly- constructed balance the beam should rest in a horizontal position when the scales are either empty or loaded with equal weights, and any slight addition of weight put into either scale should cause the beam to deviate from the horizontal; this is called the sensibility of the balance. The arms of the beam should be inflexible, exactly similar, equal in weight and length ; and, as long as possible, the centre of suspension of the scales and the centre of gravity of the beam should be all in one straight line, and the centre of motion and the centres of suspension should cause as little friction as possible. The box-beam is the best, as with this the scales, as well as the beam, rest upon knife edges. It is evident that the balance can only be in its highest state of efficiency whilst the centres of gravity and suspension remain in the relative position above mentioned ; it will therefore hardly need my former caution to be repeated, that care must be taken that they remain so, and that the beam be never strained by over-weighting. The names and relative proportions of the weights used have been so often mentioned that I need not recapitulate them. A decimal system has been proposed, which, if uni versally adopted, would simplify matters very much. At present, the practice of buying by one system, and mixing and compounding by another, the measuring of liquids whose gravity is higher, and weighing those whose gravity is heavier, then water—to this add the customary weights and measures of some localities of various articles—form a com plete jumble, causing much confusion and inconvenience, laying the customer frequently at the mercy of the dishonest dealer. Let me caution the young beginner against the slovenly habit of guessing the quantity of any chemical needed. I have seen this practised by medical men, who certainly ought to have known better. Such a habit must always lead to uncertainty of results in photographic experiment, 'and, in medicine, to much mischief. Neither should chemi cal substances be handled, but lifted with a piece of card, a bone or horn spatula, or a strip of glass ; and it should be recollected that many chemicals act upon the blade of an iron palette or bolus knife, and, in some cases, are decom posed by contact with such, particularly if in a moist con dition ; therefore the use of iron instruments for lifting chemicals is best avoided. The division of liquids into determinate quautities is effected by measuring. The various measures of liquids are derived from the gallon as defined by the laws of the king dom, and divided by chemists as follows:—The gallon, pint, fluid ounce, fluid drachm, minim. The relative pro portions are so generally known that I shall not repeat them; but I may here observe that the minim, which is the sixtieth part of a drachm, has been taken to mean a drop, which would prove a very indefinite quantity indeed, as the drops of liquids vary very greatly in size, according to the density of the liquid and the size of the neck of the bottle from which it is poured. Such a quantity would, rightly, never be prescribed. The measures in general use in chemistry are made of glass. The usual sizes are the pint, half-pint, four-ounce, two-ounce, one-ounce, and minim. Those of a tapering form, and mounted on a foot, are the most convenient, strongest, and easiest to be cleaned. The lip should be broad, otherwise, in pouring hastily, the 221 contents are likely to be spilt. They are marked by divisional lines and appropriate signs upon one of their sides, and upon the other are parallel lines, to guide the operator in keeping the measure in level position. Should this be overlooked, the quantity of liquid measured will prove inaccurate. Should the measure be inclined forwards, there will be too little ; if backwards, too much. Hot water should never be poured into glass measures until they have been well warmed, or they are likely to be cracked. They should be well cleaned after using, and kept for use placed bottom upwards, to exclude dust. Glass rods and strips of glass are useful and necessary to assist in mixing and dis solving various chemicals. 114, High Street, Ilfracombe. ON THE EMPLOYMENT OF THE COLLODIO- CHLORIDE PROCESS AS A MEANS OF MULTI PLYING NEGATIVES* BY CARL HAACK. In the preparation of the collodion it is necessary to employ a description of gun-cotton capable of yielding a perfectly transparent film when the solution is dry; Liesegang’s papyroxyle is therefore suitable for the purpose. Of all the chlorine salts, that best adapted for admixture with the col lodion is undoubtedly chloride of calcium, inasmuch as the same is capable of being dissolved in more than sufficient proportions in absolute alcohol; chloride of strontium, chloride of sodium, chloride of ammonium, and chloride of uranium, all yield inferior results, by reason of their in solubility. In 30 cubic centimetres of absolute alcohol, 1 gramme of chloride of calcium should be dissolved, and in a further like quantity of the liquid 1 gramme of nitrate of silver. The silver is very difficult to dissolve ; for this reason, 3 or 4 drops of water should first be added to the gramme of powdered nitrate, and then the alcohol poured to and fro into the mortar until the silver has disappeared. By a lengthened preservation of the solution, the salt will be found to crystallize out, and it is advisable, therefore, to employ the liquid freshly prepared. Besides these two solu tions, there arc necessary : a solution of 1 gramme of citric acid in 16 cub. cents, of alcohol, and 1 part of concentrated ammonia mixed with 6 parts of normal collodion; of pyroxyline so much is used as will render the collodion of a syrupy consistence. It is by no means immaterial in what order the different solutions are mixed. In the first place, 35 cub. cents, of ether are taken, and in this is dissolved (adding a little alcohol if necessary) 1 to 3 grains of gun-cotton, or papy roxyle ; 6 cub. cents, of the chloride of calcium solution is then added, and likewise a little alcohol in the event of any turbidity appearing. Thirty-five cub. cents, of silver solu tion is afterwards slowly poured in, the liquid being stirred the while, and the requisite quantity of pyroxyline (about 25 grains) dissolved in the mixture. For every 70 cub. cents, of liquid, 2 cub. cents, of the citric acid solution is finally added, and the collodion is then in a proper state for employment in the production of prints transferable upon porcelain or other basis. For the purposes of multiplying negatives, more opacity is required in the shadows of the diapositives, and this, as likewise increased sensitiveness, is obtained by the addition of 1 drop of the ammonia-collo- dion for every cub. cent, of the mixture. If by this means the film becomes grainy, only half the above quantity of ammonia-collodion must be added. After the addition of ammonia, the collodion is dis possessed of its keeping qualities, and for this reason it is best to mix sufficient only for the day’s requirements. To prevent the separation ot the picture from the glass, the latter should receive a previous coating of albumen; a quantity of pure white of egg is mixed with twice its volume * Read before the Vienna Photographic Society.
