Patented Nov. 15, 1938 2,136,483

UNITED STATES PATENT OFFICE 2,136,483. METHOD AND MATERIAL FOR PREVENTING THE TARNISHING of SILVERWARE Kenneth H. Barnard and Arthur F. McLean, Andover, Mass, assigaors to Facific Mills, Lawrence, Mass., a corporation of Massachus setts No Drawing. Application November 13, 1937, Serial No. 4486 m 4 Claims. (CI, 23-241). a This is an improvement on the method and ammonia of 26° Baumé. Add water to make the material patented by Grinnell Jones of Cam Solution up to ten gallons, or more or less accord bridge, Mass., Patent No. 1,766,646, June 24, 1930, ing to the silver concentration desired. Then pad for preventing the tarnishing of silverware. the cloth, which may be double-napped flannel 5 The Jones patent described a fabric for pro previously dyed, with this solution. The squeeze 5. tecting silverware from tarnish comprising a rolls of the padder will remove the excess of material, Suitable for wrapping, impregnated with liquid and the cloth may then be dried, prefer finely divided silver, or a compound thereof, which ably on a tenter frame in a current of warm air. WOuld Combine With the tarnishing gases in the The annonia evaporates, whereupon the silver O atmosphere and thereby protect the silver phosphate, being insoluble in water, is precipi O Wrapped in the protecting material. tated in the cloth in a finely divided state. The Jones patent describes a fabric impreg We then wash out the Sodium nitrate, the nated with silver or a silver compound to protect Other product of the reaction of Silver nitrate silver from tarnish. The specific example is dark and trisodium phosphate, in cold water and the 5 brown, Very powerful in color and will overpower cloth is thus left impregnated throughout with 5 other dyes and moreover is somewhat dusty and finely divided silver phosphate in amount corre uses a large amount of silver. Much of it has Sponding to the strength of the solution used, been used commercially. somewhat yellowish in color, as the protective Barnard and Kane Patent No. 2,003,333, June material. If desired the Sodium nitrate may be 20 4, 1935, describes a fabric impregnated with silver washed out of the precipitate before the precipi 20 ferrocyanide which is an improvement in vari tate is dissolved in ammonia. OuS Ways on the dark brown fabric described by If the color of the protective cloth is to be JOneS. The Barnard and Kane fabric has been brown, the uSual color, the foregoing process is Successful in commercial use, also. very satisfactory. The protective cloth, if beaten, While the cloth impregnated according to Will not give out any substantial amount of dust 25 Patent No. 2,003,333 is successful in protecting and the Silver gives the protection desired, as silver and has advantages over Jones' dark brown stated in the Jones patent. fabric it has the serious disadvantage that a part In some cases, however, the yellow silver tri of the in pregnating material is readily driven off phosphate may be undesirable as, for instance, 30 as a dust and thus silver is Wasted and further if a white or light-colored protective cloth is de 30 more, much silver is necessarily wasted in the sired. In Such cases. We use the same amount of proceSS of manufacture. sodium tetraphosphate (Na,6P4O13) and proceed as Our invention is also an improvement in other above stated. The silver tetraphosphate is white Ways Over the Grinnell Jones invention and the and will operate substantially as the triphosphate 35 invention of Patent No. 2,003,333. does. 35 Ol invention, in brief, consists in impregnat The cloth used and particularly described in ing the cioth to be protected. With a clear Silver the Jones patent, namely that precipitated from containing Solution Soluble in a Wolatile liquid, as silver nitrate by sodium carbonate, gives out a ammonia, which thus permeates the entire cloth. dust which is wasteful and dirties the hands of 40 When the volatile Solvent evaporates it precipi the operatives. Ferro-cyanide gives forth even 40 tates the silver salt in the material. In Conse more dust. quence little or none of the silver salt is lost in Various devices may be used to decrease the the process of manufacture and little or none amount of dust given or rubbed off from the Of the silver salt is lost as a dust when the fabric silver oxide cloth and the silver ferro-cyanide 45 is handled. cloth, but the cloth impregnated according to the 45 This principle may be carried out in many Ways, present invention is very much better than any of which the following is an example: way now known to us for diminishing the dust in First take five pounds of silver nitrate Crystals the silver oxide and the silver ferro-cyanide im dissolved in three gallons of Water and three and pregnated cloths. Furthermore, the advantages 50 one-half pounds of trisodium phosphate dis of having the silver Salt precipitated within the 50 Solved in three gallons of Water; mix the tWO fibres of the cloth in the manner shown makes a solutions (which may be done in tubs). This Will saving in the amount of silver required as all precipitate a yellowish white silver phosphate; the silver not taken up by the fabric may be add enough ammonia, to just dissolve this precipi used again as a part of the liquid used for 55 tate. This will require about one gallon of aqua impregnating a further batch of cloth. 2. 2,136,488 As stated, in the previous patents the amount impregnated with a phosphate of silver So as of Silver to be used per yard of cloth may be sociated with the fabric as not to give forth a varied within wide limits so that the above con dust in material quantities by ordinary handling. centration of Silver need not be followed closely. 2. A fabric for protecting silverware from tar The amount of silver required depends to a con nish comprising a fibrous material impregnated 5 siderable extent upon the conditions to which the with silver triphosphate so associated with the cloth is to be subjected in use, especially as to fibres as not to give forth a dust in material the amount of Sulphurous gases in the air to quantities by ordinary handling. which the cloth. is subjected, and the length of . ... 3. The method of impregnating a fabric with 10 time protection is desired. . . . - - a silver phosphate which consists of precipitat 10 We have described the use of ammonia as the ing a silver phosphate insoluble in water by a Volatile Solvent because that is, by far, the Sim Suitable phosphate, dissolving the precipitate in plest solvent which will dissolve the silver phos-. aqua, annonia, impregnating the fabric with the phate or silver tetraphosphate, but any suitable dissolved precipitate, allowing the aqua, ammonia, 5 volatile solvent which will dissolve the silver to evaporate, thus precipitating the silver phos 5 containing Salt and evaporate quickly to precipi phate in the fabric and washing out the water tate it can be used. . - soluble chemicals from the fabric. Furthermore, our invention is used if the 4. The method of impregnating a fabric with method of impregnating the cloth by soaking a silver salt which consists of precipitating a sil 20 it. With a silver-containing material insoluble ver salt insoluble in water by a suitable chem 20 in water, dissolved in a volatile chemical which ical, dissolving the precipitate in aqua ammonia, will precipitate the silver-containing salt in the impregnating the fabric with the dissolved pre fabric on evaporation is employed. cipitate, allowing the aqua ammonia, to evap The word "fabric' is broadly used to include orate, thus precipitating the silver salt in the any kind Of cloth, paper or fibrous or cellulosic fabric and Washing out the water soluble chem 25 material. icals from the fabric. We claim: 1. A fabric for protecting silverware from tar KENNETH. H. BARNARD. nish comprising a material suitable for wrapping, ARTHUR. F. McLEAN.

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