150 



KNOWLEDGE & SCIENTIFIC NEWS. 



[July, 1905. 



dissolve, and the copper is very likely to be damaged 

 at the same time. In order to steel face an electrotype, 

 the surface is thoroughly cleansed from all traces of 

 grease and made the cathode in an iron bath; a typical 

 solution is one consisting of 100 grm. of ammonium 

 chloride and 1J5 grm. iron sulphate, or 150 grm. iron 

 ammonium sulphate in one litre of water. Generally 

 a high current density is employed for one or two 

 minutes, after which a current of 0.4 ampere to the 

 square decimetre is employed for about five or 10 

 minutes, when the stereo is removed and carefully 

 washed and dried. Nickel facing is done in the same 

 manner, a nickel bath being employed in place of the 

 iron bath, and the stereo left in for from seven to to 

 minutes. 



Reproduction of Gramophone Records. — .As an illustra- 

 tion of the extreme accuracy of the impressions ob- 

 tained by electrolytic means, the reproduction of gramo- 

 phone records might be mentioned. As is well-known, 

 the original gramophone record is made on a wax or 

 composition cylinder, the mechanism of the instru- 

 ment causing impressions of various degrees of fine- 

 ness to be made upon the cylinder, the thickness de- 

 pending upon the tone and pitch of the sound to be 

 reproduced. Now, of course, the least fault or un- 

 evenness in the reproduction would completely ruin the 

 record. In reproducing a record in copper the wax 

 cylinder is carefully graphited and then, after being 

 connected by means of conducting wires with the nega- 

 tive pcle of the source of current, placed in a rapid de- 

 positing bath, where it is left for from 70 to 80 hours, 

 a current of from three to four amperes per square 

 decimetre being employed. By this means a good 

 thick negative is obtained which can be used for pro- 

 ducing duplicate copies of the original voice. 



Dentistry. — Electrotyping is also employed in 

 dentistry for producing mouth plates, &c. A model 

 of the part of the mouth for which a plate is required is 

 taken in wax and a plaster cast obtained from the wax 

 model. The .plaster cast is then prepared as already 

 described, and placed in a silver bath, a silver electro- 

 type being prepared; when the silver deposit is suffi- 

 ciently heavy the model is placed in a gold bath and a 

 heavy coating of gold deposited upon it. Drs. Pfan- 

 hauser and Hillischcr have also experimented success- 

 fully with pure nickel in place of silver or gold. 



Deposition upon Flowers, &e. — I will conclude this 

 article by describing an interesting and artistic method 

 for coating plants, leaves, or even insects with metallic 

 deposits. A flower or leaf will not, under ordinary 

 circumstances, conduct the electric current, therefore 

 it is not possible to coat it with metal. It is, however, 

 possible to render the surface conducting by chemical 

 means in such a manner that the structure of the leaf 

 is not spoilt. If a leaf is dipped into an ammoniacal 

 solution of a silver salt and then exposed to the fumes 

 of phosphorus, the phosphorus reduces the silver salt, 

 and the whole surface becomes coated with a very thin 

 film of metallic silver. The surface of the leaf is now 

 conducting, and if a wire is fastened to the stalk and 

 the leaf placed in a copper-plating bath, a coating of 

 copper of any desired thickness can be deposited upon 

 the leaf. \ better method is to dip the leaf or flower 

 into an alcoholic solution of silver nitrate and to then, 

 after draining off the excess of the solution, exoo.se to 

 the action of sulphuretted hydrogen gas. By this 

 means a thin and homogeneous film of silver sulphide — 

 which will conduct the electric nirrtnt— is obtained. 

 The leaf is now placed in the depositing bath and coated 



with copper or silver as the case may be. If the opera- 

 tion is carefully carried out with a very low current 

 and only a thin coating of metal deposited, all the vems 

 and markings of the leaf remain. Leaves, flowers, 

 and even insects, such as beetles or flies, when coated 

 in this way can be kept for years without withering or 

 decomposing. Of course, the actual leaf or insect is 

 not seen, but is covered with a metallic shell which 

 almost exactly represents the original. 



Star Map.— No. 3. 



Cetus, Erida.n\is. 



The constellations here shown are of no special in- 

 terest. It may he noticed that there are two boundary 

 lines dividing Forna.x from Eridanus. The enclosed 

 portion is included in the latter constellation by Pro-tor 

 and some others, but,accordingt:omostauthorities(incli:d- 

 ing Gould) belongs to Fornax, and is lettered accordingly. 

 The star at the top of the map marked m is included by 

 Proctor (and B.A.C.) in Aries, but other authorities call 

 it M Ceti. 



" Piscittm (I. h. 56 m. + 2"^ 14.'), a double star of magni- 

 tudes 3 and 4. Distant 3A". 



o Ceti (Mira) (II. h. 14 m. — 3° 23') a remarkable 

 variable, usually varying from about 3rd magnitude to 

 9th. Though it has long been known, iiaving been one 

 of the first variables noted, it is still an enigma. Its 

 period seems to vary grtall)', but is usually about 

 331 da)S. In 1779 it was estimated as ist magnitude; 

 in ib68 it never attained more than 5th magnitude. 

 Daring the last twelve periods the magnitude at maxi- 

 mum has varied from 2'5 to 4-7. The spectrum shows 

 no signs of the star being double, and the variability 

 is probably due to its own disturbances rather than to 

 any outside cause. 



7 Ceti (II. h. 38 m. -|- 2° 46'), a double star, distant 3i". 

 One of 3rd magnitude, yellow; other of 6th magnitude, blue. 



e Eridani (II. h. 54 m. — 40^ 45')> ^ double star, dis- 

 tant 8-2". Magnitudes 3* and 5^. This star is supposed 

 to have dwindled considerably in magnitude, having been 

 classed as ist magnitude in the time of Ptolemy, though 

 now considered as 3-06. 



With our special number for the British .Association 

 meeting will be issued Map No. 12 (South Polar Regions), 

 which should prove of use to those visiting South Africa. 

 With the August number, Map No. 6 (Leo and Cancer) 

 will appear, which will show the region around the sun 

 at the time of the coming eclipse. 



The Word "Patent." 



To THE EuiTOltS oi- " Knowi.i-.ijoi.." 

 Sirs, — The word " Patent " is one of those curiosities of the 

 li^Dglish languaf^e which tend to make it so puzzling to 

 foreigners, and even to ourselves. Now this word is perhaps 

 most generally pronounced f'aylcnt, but in the profession it is 

 more usually referred to as I'altcnt. There is one reason 

 which I should like to point out in favour of using the former, 

 and that is the confusion that is sometimes caused in mistak- 

 ing the latter pronunciation for the word " Pattern." Jones 

 may say, "That machine is my pattern," and Brown may later 

 say, " That machine is Jones's patent, I heard him say so him- 

 self." When shall we take to teaching phonetics? 



Vours faithfully, 



K. 



