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bismuth, or lead. In such a case, use al Dipping in Aquafortis and Soot. newly-made dipping bath and a small | After rinsing in fresh water, the articles proportion of acid. Articles which are well shaken and drained, and then have been cleansed by alkalies must be plunged into a bath composed of nitric washed before being put into the dipping | acid at 36o Baumé, 100 parts; common bath, or pickle. Thoroughly and rapidly salt, 1 part; calcined soot, 1 part. This rinsing in fresh water all the articles, mixture attacks the metal with the before and after each of the following greatest energy, and the pieces should operations, must be strictly attended to. therefore not remain in it more than a The various manipulations which com- few seconds. The volume of acid should plete the cleansing succeed each other be about 30 times that of the articles to without interruption; and the articles be cleaned, in order to prevent too great must be stirred as well as possible an elevation of temperature due to the in the acid baths, and in the rinsing chemical reaction, which would result in water. After dipping and rinsing, the the rapid weakening of the acid. After various pieces are fixed to a brass wire, this bath, and rapid rinsing, in order to or hooked upon brass or copper hooks, prevent the production of nitrous vapours Small articles of jewellery are suspended the pieces present a fine red lustre, gold to a stout copper wire. These hooks are 1 yellow or greenish yellow, according to better if made of pure copper than of the alloy employed, and such as to make brass, and it is still better to use glass one believe that they are entirely cleansed hooks, which are cheap and are not cor- of foreigo matter; yet if the pieces in roded by the acids. Such nooks or sup- this state are plunged into a gilding or ports can be made by bending glass rods, silvering bath, they become entirely black, by the heat of a charcoal fire, or of a gas and without any metallic lustre. "If the burner, to the desired shape. Those ob- pieces are put aside without rinsing, there jects which cannot be suspended or at- rises on their surface a green froth and tached to hooks, are put into perforated nitrous vapour, which indicate the decomladles of porcelain or stoneware. It is position of the acid with which they are less economical, but sometimes absolutely contaminated. When the vapours have necessary, to use baskets of brass or copper disappeared, the pieces, even after washwire cloth. Those who frequently have ing, remain of a dull black, on account of to cleanse, very small articles will find it the formation of a basic copper salt which advantageous to emp.oy a basket of pla- is not soluble in water. This last mode tinum wire cloth, which, although ex- / of operating, called blacking by aquapensive in the first cost, will be found fortis, is preferred by a few gilders, varcheaper in the end, as it is almost inde- nishers, and colour fixers, who find it structible.

economical to allow the production of Dipping in old Aquafortis.-If there nitrous vapours while the pieces are is any aquafortis, nitric acid, already draining on top of the vessel which conweakened by preceding dippings, plunge tains the acids. Any subsequent operainto it the articles which have passed | tion is to be prefaced by a rinsing in fresh through the sulphuric acid pickle bath, water. When small objects, such as pins, and have been rinsed. They may remain caps, or eyelets, are to be dipped, they are there until the red coat of protoxide of put into a stoneware pot, with a small copper has entirely disappeared, leaving, quantity of aquafortis, and then rapidly after rinsing, a uniform metallic lustre. shaken and stirred. In this case the The dipping in old aquafortis, though not acid is entirely used up with the producabsolutely necessary, is recommended for tion of abundant vapours, and the objects two reasons; it economizes the cost of remain blackened, and ready for a further fresh acids; and, as its action is slow, it cleansing. Care must be taken in the prevents the too rapid corrosion of the choice of aquafortis. Three kinds of cleansed copper during the time of the nitric acid at 36° are to be found in the solution of the protoxide.

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is straw yellow, and another which is | mon salt, 1 part. In preparing this of a more or less dark-red colour. The bath, nitric acid is first put into the white acid, without nitrous gas, does not vessel, and then sulphuric acid, which is cleanse well, especially when freshly much denser, and would not mix readily used. The red acid acts too powerfully if it were put in first. At the time of and pits the copper. The straw-yellow mixing, especially when the salt is added, acid is preferred to the others. Nitric considerable heat and a quantity of acid acid at 40° is too energetic and costly; and injurious fumes are produced, so that however, certain operators who have | it is prudent to operate in the open air, W cleanse large quantities of copper or under a good chimney-hood with a wares prefer it on account of the rapidity movable glass sash. As these acids must of the operation. The acid is spent when be employed cold, it is necessary to preits action on copper goods becomes too pare them in advance. Copper articles, slow, and when the objects removed from after this dipping, are lighter coloured the bath are covered with a kind of and much brighter than after the passage bluish-white film. Such acid is preserved through aquafortis. They may then be for the preceding operation, namely, dip- considered as completely cleansed, and ping in old aquafortis; or for dipping in must be immediately rinsed in plenty of the whitening bath. Very good aqua clean water. The above acids are too fortis may cleanse imperfectly when the energetic for small articles, such as pins temperature is too low or too high. This or hooks, which are generally cleansed accounts for the difficulty of cleansing in in stoneware colanders. As the number frosty weather, or during the great heat of small articles stop up the perforations, of summer.

the acid cannot run out so quickly as Aquafortis for Bright Lustre.—There desired, and begins to heat and give off is an excellent way of obtaining a bright fumes, and the pieces blacken before they lustre for any pieces, the surfaces of can be rinsed. Therefore, for small pieces, which have been dulled or slightly pitted add to the above mixture one-eighth of by a defective cleansing, or by their pas- its volume of water. Place the articles in a sage through the acids for removing gold stoneware pot; stir rapidly with a small or silver. Place them for a few minutes quantity of bitters, as the last mixture in a bath composed of old aquafortis, is termed, and then the whole is plunged nearly spent, 1 part; hydrochloric acid, into a quantity of fresh water as soon as 6 parts; water, 2 parts. The pieces, the acid has sufficiently acted. This when removed from the bath, are entirely method is not economical, as the acid is black, and must be thoroughly rinsed in lost; but the dipping liquors do not bewater to remove the kind of black mud come heated. which covers them. They are then Whitening Bath consists of old aquacieansed and dipped again. This bath fortis, sulphuric acid, common salt, and will be found useful by electro-gilders. uncalcined soot. Pour into a large stoneIt is also convenient for removing the ware vessel a certain quantity of old end adhering to the castings of copper aquafortis from previous dippings, and alloys. Large pieces may remain in the then add twice the volume of sulphuric bath for 20 or 30 minutes, as this mix- acid at 66o. The mixture is allowed to ture acts very slowly on copper and its cool off until the next day. The nitrate alloys.

of copper of the old aquafortis becomes Dipping in Compound Acids for a converted into sulphate of copper, which, Bright Lustre.—These acids are of two by cooling, crystallizes against the sides kinds, according to the object in view. of the vessel. Decant the liquid portion If the pieces are to have a bright lustre, into another vessel, and then add 2 or they are stirred for 1 or 2 seconds in a 3 per cent. of common salt, and as liquid, prepared the day before, and cold, much of calcined soot. This mixture is made of nitric acid at 36°, 100 parts; much less energetic than the compound sulphuric acid at 66°, 100 parts; com- / acids for a bright lustre, and often re

places them advantageously. The crys. | 2 seconds, and a last rinsing, it becomes tallized sulphate of copper is collected clear enough. and sold. This bath is strengthened, Dipping in Nitrate of Binoxide of Mer. when necessary, by the addition of cury.—This operation consists in plungstronger aquafortis and oil of vitriol. To ing the cleansed articles for 1 or 2 replace the portion used up during the seconds into a solution of water, 24 galday, equal quantities of old aquafortis lons; nitrate of binoxide of mercury, a and oil of vitriol are added at the end of third of an ounce; nitric acid or, prefer. the day. The next morning the liquors ably, sulphuric acid, two-thirds of an are decanted, and the sulphate of copper ounce. When nitrate of binoxide of is gathered. Soot and common salt in mercury is poured into the water, a thick sufficient proportions are then added. cloud is formed, of a yellowish-white In this manner a perpetual and cheap colour, which subsequently disappears. whitening bath is prepared.

Stir the mixture before using it. The Compound Acids for a Dead Lustre proportion of mercury salt above-named If it is desired to give the objects a dead must be modified, according to the size lustre, they are, after dipping in aqua- of the pieces, and the nature of the alloy. fortis and rinsing, plunged into a bath, Thus less mercury will be used for light prepared previously, composed of nitric pieces of jewellery which need a very thin acid at 36", 200 parts; sulphuric acid at | deposit. On the other hand, more mer66°, 100 parts; common salt, 1 part; cury is required for heavy objects, such sulphate of zinc, 1 to 5 parts. Copper as table ornaments, which should receive articles may remain from 5 to 20 minutes a thick deposit of gold or silver. The in the cold bath, and the dead lustre will latter must come from the mercurial sobe the more apparent, the longer the lution with a perfectly white and bright immersion has been. From this bath, appearance, looking like silver, whilst after a long rinsing, the objects have an the colour of the light articles is scarcely earthy appearance. This dulness is re- changed. After a perfect cleansing, the moved by a rapid passage of the pieces pieces will, after passing through a strong through the compound acids for a bright mercurial solution, be perfectly white lustre, and by an immediate rinsing. If and bright. But there will be a cloudy they remain too long in the latter acids, appearance, or various shades of colour, the dead lustre will disappear, and the if the cleansing has not been properly operation for dead lustre will have to be done. The amalgamating bath becomes repeated. If a bath for the bright lustre spent by use; it may be revived by the is not at hand, the objects, after rinsing, addition of a few drops of nitrate of may be rapidly passed through the dead-mercury; but it is better to prepare a lustre bath, which will remove the dul fresh one. No intervals must be allowed ness of the lustre caused by too long between the various operations of cleansimmersion. After long use, the com- | ing. The dipping baths are ordinarily pound acids for a bright lustre may be held in vessels of glass, stoneware, por. employed in a certain measure for a dead- celain, or of any other material which lustre bath. The mode of operation resists the corrosion of acids. Common remains the same. For large embossings earthenware and that with a lead glaze for furniture, or for some clocks, a hot must be carefully avoided. The dipping bath for dead lustre is used, composed as i pots must be rather high, and be furfollows ;-Old aquafortis, about 4 to 5 | nished with a cover, in order to prevent parts; sulpauric acid, 1 part; sulphate evaporation. Those with ground edges of zinc, 8 to 10 per cent. The sulphate may be covered with a pane of glass. of zinc is gradually added when required, wide open-mouthed earthen pans are for increasing the deadness of the lustre. very good for rinsing. A large hood, The lustre thus obtained appears dull and communicating with a chimney, and yellowish ; after a thorough rinsing, a closed with a sliding glass sash, should conpassage through th: same bath for 1 or | tain the following apparatus for complete

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