^ 



oi.. XXIII. No. 2.] 



POPULAE SCIETTCE I^EWS. 



21 



Practical Cljonjistry arjd tlje ^rts. 



ELECTRO-PLATING AND ELECTRO- 

 TYPING. 



^V'llen a current of electricity is passed 

 through water, decomposition of the liquid 

 iakes place, and bubbles of hydrogen gas 

 Sippear at the negative pole and oxygen at 

 ■the positive. Like many other electrical and 

 chemical phenomena, we cannot explain this 

 tion, but only know that it. is so. 

 Likewise, if the electric current is passed 

 rough a solution of a salt of copper, silver. 

 Id, nickel and many other metals, the salt 

 decomposed, the acid element set free at 

 le positive pole or electrode, and the metal 

 eposited upon the negative one. If, instead 

 of the usual wire for conveying the current 

 into the solution, we use a metallic vessel or 

 utensil, the metal will be evenly deposited 

 over the entire siuface, or, by using a mould 

 Co^■ered with some substance that is a good 

 conductor of electricity, we can obtain a per- 

 t copy of it in the deposited metal. 

 This electrical deposition of metals has be- 

 pme a very large and important industry, 

 means of it we can cover the cheaper 

 Is with a brilliant and unoxidizable coat- 

 of gold, siber, nickel or any desired 

 1. Nearly all the plated ware in use is 

 Sde bj- ihhr process, the practical details of 

 which may be of interest. 

 I In plating \v-ith silver the liquid used is a 

 ' solution of chloride of silver jn cvanide of 

 potassium. A large vessel is filled with it, and 

 tlie articles to be plated suspended in it from 

 a copper rod laid across the top and connected 

 with the negative pole of the source of elec- 

 tricity. To a second copper rod, connected 

 with the positive pole, plates of silver are 

 attached and also immersed in the solu- 

 tion. As the silver is deposited at the nega- 

 |ti\c pole, more silver is dissolved from these 

 plates by the acid set free at the positive pole, 

 and thus the strength of the solution is kept 

 ciiiistaut. 

 ■ It is necessary to clean the articles very 

 carefully before immersing in the plating so- 

 lution, as the slightest trace of dirt or grease 

 wiiuld interfere with the regular disposition 

 of silver and render the work imperfect. This 

 is ertected by mmierous scourings, brushings 

 and dippings into acids and alkalies. The 

 source of the electricity was formerly the gal- 

 vanic battery, but the recent improvements 

 ' in electric dynamo machines have rendered 

 them especially applicable to this work, and 

 they are rapidly supplanting the old-fashioned 

 Miltaic cells. 



When everything is ready, a very strong 

 I rent i» sent through the plating solution, 

 for the purpose of quickly depositing a thin 

 layer of silver. This process is called "strik- 

 ing," and after it is effected a weaker current 

 is used and the silver deposited more grad- 

 ually. The current is continued until the 



required weight of metal is deposited, accord- 

 ing to the thickness of the plate desired. An 

 ingenious arrangement is in use by which the 

 articles to be plated are suspended from one 

 arm of a balance which forms a part of the 

 electric circuit. The balance is weighted ac- 

 cording to the amount of silver desired, and 

 as soon as it is deposited the beam turns, 

 breaking the circuit and stopping all action at 

 once. When the plated articles are first re- 

 moved from the solution they do not show the 

 familiar lustre of silver, but the finely divided 

 metal upon their s'urface gives them a dead 

 white appearance like porcelain. This is 

 easily removed by polishing and burnishing 

 wheels, and the bright "electro-plate" is 

 ready for the work of the engraver or deco- 

 rator. 



Gold and nickel plating are done by prac- 

 tically the same process. A solution of chlo- 

 ride of gold in cyanide of potassium is used 

 for gold plating, and a small plate of gold in- 

 stead of silver is suspended in the solution at 

 the positive pole. Nickel plating is a more 

 recent invention, but is effecte 1 in the same 

 way, and has become an immense and profit- 

 able industry. It is equal to silver in beauty 

 and brilliancy, and has superior resistance to 

 those impurities in the air which tarnish and 

 discolor the more expensive metal. 



Electrotyping is a modification of the same 

 process, by which any number of reproduc- 

 tions of a "form" of type can be obtained in a 

 solid block of metiil, thus saving the wear of 

 the type aud allowing it to be distributed and 

 used for other work. After the type is set up 

 into a "form," a wax mould is taken of its 

 surface. The face of this mould is dusted 

 with finely powdered graphite or black lead, 

 to render it a conductor of electricity, and it 

 is then suspended in a solution of sulphate of 

 copper, so as to form a part of an electric cir- 

 cuit. Metallic copper is deposited upon the 

 face of the wax mould, giving a perfect re- 

 production of the original form of type, and 

 when it has reached the requisite thickness it 

 is removed, strengthened with a backing of 

 type metal and mounted upon a block of wood 

 or metal ready for use in the printing press. 

 This process is a very cheap one, and where 

 a large number of copies are to be printed 

 prevents the rapid wearing out of the expen- 

 sive type. Wood engravings are always 

 printed from these electrotype reproductions, 

 as the soft wooden block would be rapidlv 

 destroyed in an ordinary printing press. In 

 the process of stereotyping, the plates are 

 cast directly in type metal from a mould of the 

 original type in plaster-of-Paris or paper pulp, 

 but, except in the case of daily newspapers, 

 or for inferior work, the electrotype process 

 has nearly superseded it. ' 



HANDLING OF ACIDS. 

 When emptying carboys of acid, see that 

 they are securely held. Do not tilt them 



over with one hand, while holding a receiving 

 vessel in the other, unless they are so hung or 

 placed that you have absolute control over 

 them. A good way is to put the carboy on 

 an elevated place, say about iS to 24 inches 

 high, so that when it lies on its side, its upper 

 edge will be about three inches within the 

 edge of the platform. If the carboy has a 

 wooden strip or side rail, instead of a handle, 

 it is best to tilt it on the side where this is sit- 

 uated, as this assists in keeping command 

 over the carboy while it is tilted. If you 

 have a carboy swing, be sure and see that 

 the carboy is securely fastened, and that al- 

 lowance be made for the change in the center 

 of gravity as it becomes more empty. 



Never stand in front of a carboy while 

 emptying it, but sidewise, and use a receiving 

 vessel with a substantial handle. Do not 

 hold a bottle with a fuimel under the mouth 

 of the carboy, nor hold any vessel so that if it 

 should overflow, the acid would run over 

 your hands. 



Choose such a place for emptying carboys, 

 or any other containers of acid, as will suffer 

 the least injury should the vessel be broken, 

 or any of the acid be spilled. 



Remember that the larger or the flimsier 

 the container is, the more care and circum- 

 spection must be exercised. A person may 

 have emptied a hundred or more carbovs 

 without any mishap, when unexpectedly an 

 accident will happen, and in nine cases out 

 of ten this is due to pure carelessness. 



Never carry large containers of acid in con- 

 tact with your body. Should they accident- 

 ally break, a most painful burn (sometimes 

 turning out fatally) may be the result. 



When opening acid bottles, for instance the 

 usual five pint sizes, first remove the cement 

 from around the stopper, and wash and wipe 

 the neck carefully to remove everv trace of 

 foreign matter. Then, if the stopper cannot 

 be easily loosened by hand, place a coarse 

 towel over the stopper and bottle, and while 

 bearing with the thumb of one hand against 

 the edge of one side of the stopper, tap the 

 other side gently with the wooden {no^ me- 

 tallic) handle of a spatula, when it usually 

 will become loose. Should it be very obsti- 

 nate, and the bottle at the same time appear 

 to be of rather thin glass, place the bottle into 

 a sufficiently deep and huge acid-proof jar to 

 receive the contents in case the bottle should 

 break. The reason why a towel should be 

 put over the stopper is almost self-evident. 

 If a bottle of acid is exposed to a warm 

 temperature, evidently some pressure will be 

 developed within the bottle. Bv moving the 

 bottle about, the neck and bottom of the 

 stopper will be wetted with the acid, and if 

 afterwards the stopper is suddenly loosened, 

 the compressed air or gases will throw out 

 any particles of liquid which are between tha 

 neck and stopper. 



