In small establishments one large tub, to form the receptacle for all spent or used-up liquids, will be found sufficient; but in large places several will be required. In the former case the water is only drawn off at the beginning of every fresh week, which allows plenty of time for the precipitation of the silver without any disturbance taking place in the mixture between the close of one week and the commencement of another; whereas in large concerns it requires to be drawn off continually unless other vessels are provided for its reception during a long period. Attempts have been made to recover the silver from these solutions by simply filtering the liquid through a coarse piece of felt or flannel; or by providing a false bottom in the tub or other vessel containing the waste waters, arranged in the following manner:—A tolerably large tub would be employed, being about one-fourth filled with coarse deal sawdust, next would be placed the false bottom perforated with numerous small holes, and upon this would be firmly secured a piece of felt, so as to exactly fill up the space in that part of the tub, which then serves to act as the filterer of all solutions poured in above. The liquid after passing through the piece of felt proceeds through the perforations in the false bottom into the sawdust beneath, where it is allowed to run away by means of a small hole or tap at the bottom. But the use of either of these processes, if adopted on a large scale, where the waste products amounted to some hundreds per annum, would be wretchedly bad economy and tend to a serious loss of valuable metal; the boiling sulphuric acid, used in cleansing the work and for other purposes, has the power of dissolving minute particles of silver as well as those of the baser metal which always enters into the composition used in the production of the work of the silversmith; therefore, that portion of the metal which has become dissolved and entered into the chemical state, requires to be brought back to its original form before it can be saved by such means as those just described. To illustrate this more clearly, we will take the process of gold-colouring. If workmen were to notice the rinsing waters employed in this process, subsequently allowing the vessels containing the rinsing to stand for a very short time, upon pouring away the surplus water, a white curdy precipitate will at once be observed at the bottom. This is the silver removed from the surface of the gold alloy, which has been precipitated by the muriatic acid and the common salt employed in the colouring mixture, into the form of chloride of silver. Now in this proceeding there is no gold to be seen in any of the vessels, but it is a well-known fact that a portion has been removed during the process from the surface of the gold articles. Where is it? Why, it has become dissolved, and is therefore held invisible in the solution, in consequence of the colouring mixture forming the well-known solvent for gold, aqua-regia. This is exactly the case with a portion of silver in the silversmith’s solutions; small particles are continually being dissolved by the mixtures employed, and are thus held in solution past the power of filtering, unless some chemical ingredient be added to it, which acts as a re-agent upon the metal sought to be recovered. From what we have seen in the colour water, which always contains a little silver, it is evident that both muriatic acid and common salt will do this work for us. We prefer common salt, on account of its cheapness, besides being easily procurable.
The best mode of treatment for the silversmith’s waste waters, after being collected together by pouring into the receptacle specially provided for that purpose, is to prepare a saline solution for the precipitation of the silver. This may be made by mixing together common salt and tepid water, in the following proportions:—
Common salt 3 oz.
Tepid water 1 pt.
The water need only be sufficiently warm to dissolve the salt, and the proportions given do not require to be strictly adhered to; in fact any quantity, if properly mixed, will do to effect the purpose required, and we merely give these as a guide for the process. In small establishments where only one tub is employed, the above proportion of saline solution may be added (every Saturday after the completion of the day’s work) to the waste-water; the whole should then be stirred slowly in a circular direction, and allowed to settle until Monday morning, when all the surplus water may be drawn off and poured away. In larger establishments the accumulation of waste-water is greater, therefore several collecting vessels should be employed, and the mixture for precipitation may be added to them at other times than those stated, if required, and in accordance with workshop regulations. The sediment produced in the collecting vessels after the supernatant water has all been drawn off, may be removed, dried by heat in a strong iron pan, and subsequently sold to the refiner.
Licences and Duties.
Manufacturing silversmiths, and all persons trading in silver wares of more than five pennyweights each, are compelled to take out a licence; articles under that weight being exempt. The licence has to be taken out annually, and costs £2 6s. for manufacturing or trading in articles under thirty ounces in weight, and £5 15s. for articles of thirty ounces and upwards. It should be taken out on the 6th day of July in each year at the Excise Office. This Act of the Legislature was passed in the year 1803, 43 George III. c. 69, and is not the only one which refers to the subject we are now considering. There are other conditions besides the compulsory Plate Licence, as it is called, to which manufacturing silversmiths are subject, such as the supervision of the assay offices, in the case of certain descriptions of goods; and the payment of duty on all such goods. At the present time all hall-marked silver articles have to pay a duty of 1s. 6d. per ounce, calculated not on their gross weight, but on five-sixths of the weight, the other sixth being allowed for waste in finishing the articles, as they are sent to the Hall in a half-finished state. The duty is paid at the Assay Office at the time the goods are sent to be marked. Some dissatisfaction just now exists in a portion of the trade with regard to the above duty, as it is considered excessive, besides having a tendency to discourage the manufacture of silver wares; be this as it may with respect to a certain description of goods, on the bulk of the trade it can have no injurious effect whatever. The duty is paid only on manufactured plate and such other articles as are requested to be hall-marked; besides which the trade in this particular department of manufacture has never been very extensive, being confined to a few firms of eminence only.
Before going into the general details of this question, it will be as well, perhaps, if we give a short history of the imposts that have existed in the silver trade for some time back. The first impost that we can find recorded took the shape of a duty, and was levied as far back as the year 1720, by 6 George I. c. 11, which placed a tax of 6d. per ounce on all silver plate manufactured in Great Britain, which, should be assayed or marked. The officers of the Excise were to collect the tax, but the great difficulty of ascertaining the number of ounces worked up, which the provisions of the Act did not clearly set forth, soon rendered it ineffectual, and it was consequently repealed by the statute 31 George II. c. 32, and a licence then substituted had to be taken out by manufacturers and dealers in plate. The licence at this period amounted to forty shillings, and had to be renewed annually. In 1759, 32 George II. c. 14, it was increased to £5 per annum, for every person trading in silver wares of thirty ounces and upwards; wares in one piece not exceeding five pennyweights in weight being exempted.