(g) The residues almost always exist as silver chloride. Wash by decanta-tion, with plenty of water, in a capacious vessel which can be shaken, the mass - filter-paper and all - till free from copper, etc. Next drain off as much water as possible, and add strong ammonia, and after a time filter to get a clear solution. Place this in a wide-mouthed bottle, which fit with a cork. Through the cork pass two wires, to one of which attach a cathode of a strip of silver, and to the other an anode of lead. Lastly, connect a Daniell cell, and leave to itself for a day or two. The strip of silver will then be found studded with crystals of the reduced metal, while the lead will have a scale of lead chloride, some of which may have fallen to the bottom of the bottle The ammonia is then shaken up, with the remaining undissolved residue, the lead is scraped, and the cell is recharged, when all is again ready to proceed for another two or three days. It is obvious that a bag of the washed residues can be suspended in the electrolytic bath. It is not a process to be recommended if rapidity is an object; but this is often of no consideration whatever.

I do not recommend it for large quantities, though under certain circumstances it might answer even then; but for small quantities, such as pints or quarts, I certainly do, and claim for it the following advantages: - First and greatest, Less expenditure of superintending time and trouble than any other. The time expended in preparing the ammoniacal solution is but a few minutes. That expended in charging the cell is about the same, and besides these there is absolutely nothing to do beyond occasionally scraping the lead anode and collecting the silver crystals, after the easily fitted up and simple apparatus necessary has been procured. - Second, Small cost of apparatus and materials. Those consumed are zinc, copper sulphate, and lead. The ammonia will do-over and over again, for the cork prevents its dissipation, and the loss in manipulation need be very small. Third, There is less mess and disagreeable work than any other method I know of. Fourth, The silver is obtained in a convenient form for future use, which is usually to prepare the reagent, silver nitrate. I have tried the method of reducing by means of zinc, but found these disadvantages and difficulties. First, It is not easy to ascertain when all the chloride is reduced.

Second, Washing the metallic silver powder free from zinc chloride is a matter which takes a very considerable time. Third, The process is messy and disagreeable. Fourth, The reduced metal cannot be very pure, for ordinary zinc always contains a little lead, which would remain with the silver. I have also tried reduction by means of glucose, though not very thoroughly, finding it take time and trouble. The process of reduction with soda carbonate in a crucible is the worst of all in my estimation for small quantities. The time is greater than any others, and the heating of the crucible without special apparatus is most troublesome, to say nothing of the fuel consumed. Moreover, whatever others may find, I have always observed numerous little beads of silver scattered in a most aggravating manner all over the pot, which it is impossible to collect. I may mention that by the electrolytic method described, every trace of silver leaves the solution after a time, as may be proved by neutralising with an acid. One word more.

It might be worth while dipping the ends of exposed iron into melted paraffin wax before placing in the electric bath. - (L. S. Powell.)

(r) A process invented by Stockmuir and Fleischmann and worked out by them in the chemical laboratory of the Bavarian Industrial Museum, is exceedingly simple, and is employed in many establishments. In order to remove silver from a potassium cyanide silver solution, it is only necessary to allow a clean piece of plate zinc to remain in the liquid for two days; even better results are obtained by the use of iron conjointly with the zinc. In the first case, the silver often adheres firmly to the zinc, whilst in the second it always separates out as a powder. It is then only necessary to wash the precipitated powder which usually contains copper (since spent silver solutions always contain copper), dry it, and then dissolve it in hot concentrated sulphuric acid, water being added, and the dissolved silver is precipitated by strips of copper. The silver thus obtained is perfectly pure. If the amount of copper present is only small, it can usually be removed by fusing the precipitated powder with a little nitre and borax.

In this way a spent silver bath was found to contain per litre

First experiment ..

1.5706 grm

Second „ .....

1.5694

Mean.. .. ..

1.5700

The presence of silver could not be qualitatively ascertained in the residual liquor.

(s) After soaking the prints for 5 minutes in water made slightly acid by acetic acid, remove them to another dish, and add to the water from which you have just taken them about a tea-spoonful of salt; stir it rapidly for a moment with the hand, when it becomes as white and thick as milk. This solution is then poured into a common wooden pail, which will hold enough water for the first washing of a hundred prints, and the next day, when ready to tone again, you will find that the solution has become perfectly clear, and in the bottom of the pail is a clear white sediment - pure silver chloride. Then pour off the water to within an inch of the bottom, and the pail is ready to be filled again.

On adding salt to the second water in which you washed the prints, there is hardly a trace of silver, and it is not worth saving. About once a month, pour the sottlings from the pail through a fine cloth to filter it, and throw the cloth and contents into the silver paper clippings. In this way you will save more than half the silver used in making the print. - (A. C. Hopkins.)

(t) To separate silver bromide from waste emulsion, Scola recommends that 2-3 per cent. of sulphuric acid should be added, and the mixture should be boiled for some minutes, after which the bromide settles rapidly to the bottom of the vessel. It is now washed and dried, when it is ready to be cast into sticks for use in the battery about to be described.