14 



SCIENTIFIC NEWS. 



[July 6, 1888. 



manipulation ; the hands of the men are often in con- 

 tact with the metal, and the air is filled with mercurial 

 fumes, which, it must be remembered, are given off even 

 at the ordinary temperature of this country. 



To do away with the evils resulting from this process, 

 attempts have been made to "silver" mirrors with a 

 thin film of pure silver deposited upon the glass, and 

 thus entirely dispensing with the use of mercury. But 

 these processes, though apparently successful, have dis- 

 appeared from use. It is, indeed, rumoured that the 

 inventors have been " bought off'," lest the interests of 

 the mercury trade should suffer loss. 



A considerable quantity of mercury in the metallic 

 state is used in the manufacture of thermometers, baro- 

 meters, and hydrometers, in making Sprengel pumps, 

 and in a variety of the operations of chemical and phy- 

 sical laboratories. For these purposes it is not likely to 

 be superseded 



Mercury is also employed in the preparation of ver- 

 milion, of corrosive sublimate, and of nitrate of mercury. 

 The manufacture of vermilion and its use in the fine arts 

 cannot be held injurious, since it is neither soluble nor 

 capable of being volatilised at ordinary temperatures. 



Nitrate of mercury is used to give hare and rabbit 

 skins the power of felting. For this purpose it is dis- 

 solved in water, and brushed lightly over them with a 

 sponge. In this process the hands of the workman are 

 liable to absorb some of the poison. 



The manufacture of corrosive sublimate without great 

 care is very dangerous, as this compound may quickly 

 prove fatal if inhaled in the state of vapour. Its use as 

 a disinfectant also requires no little caution. 



Antimony is one of the minor poisons from our pre- 

 sent point of view. Its only manufacturing uses of any 

 importance are in the preparation of so-called antimo- 

 nial vermilion. This colour is less beautiful than the 

 true, mercurial vermilion, but it finds a demand from its 

 low price. Neither its preparation nor its use involves 

 anything dangerous to health. 



Of much more importance is the double tartrate of 

 antimony and potash, commonly known as tartar-emetic. 

 This substance was formerly employed only in medicine, 

 but it is now used on a much larger scale, along with 

 tannin, in fixing aniline dyes upon cotton wares. It has 

 been often accused of producing irritation of the skin, 

 and even erysipelas in persons wearing cottons which 

 have been thus got up. It is, however, to be noted that 

 men employed in the manufacture of tartar- emetic and in 

 its use in dyeing and printing operations do not seem to 

 suffer in the least. The same must be said of other pre- 

 parations of antimony which have been tried as cheaper 

 substitutes for tartar-emetic. 



(To be continued.) 



Betrieb der Galvanoplastik mit Dynamo-electrischen Mas- 

 chinen zu Zwecken der Graphische Kiinste. Von Otto- 

 mar Volkmer. Vienna: A. Hartleben's Verlag. 



This handbook, one of a series of technical works 

 corresponding to the English series known as Weale's, 

 relates to electrotyping as used in pictorial arts. It 

 deals with the machinery used for eletrotyping, including 

 gas engines and dynamos, the baths used, the solutions, 

 and the methods of connecting them up and of regulating 



the current. We find descriptions of the installations in 

 Vienna at the Imperial Institute of Military Geography, 

 and at the Imperial printing establishment, of which 

 latter the author is vice-director. The fourth section is 

 really the most important in the book, as containing 

 novel information, the rest being such as could be com- 

 piled from works already existing. It deals with the 

 practical processes used for electrotyping, including the 

 production of the original plate as a mould for electro- 

 typing on, the deposition of electro-copies, the facing of 

 these with steel or nickel or brass as a hardening pro- 

 cess. The author next describes the processes of pro- 

 ducing a plate fit for printing off, from non-metallic 

 matrices, such as gelatine photo reliefs, wax and gutta- 

 percha moulds, etc., and gives a detailed description of 

 the production of the electro-plates from which the 

 Government maps of Austria-Hungary are printed. 



A descriptive list is given of the various chemicals 

 and materials used by electrotypers, with their pro- 

 perties, tests for purity, etc. 



It is a pity that in a book like this, intended to be 

 written up to date, the author should have chosen for 

 description those dynamos which are used in Austria- 

 Hungary only, a rather antiquated Gramme machine, 

 one by Schuckert, by no means his latest or best type ; 

 and one by Krotlinger, of Vienna, also containing no 

 special features, when of late such very improved 

 machines specially constructed for electrotyping have 

 come into use. An illustration is given of a dissected 

 Gramme ring, which at first looks like a very old friend, 

 but we find that the author has substituted for the iron 

 wire, of which the core is actually built, iron plates so 

 placed that, in working, strong electric currents would be 

 produced in them sufficient to damage the machine from 

 over-heating. 



In a chapter on the theory of the work done by 

 electric currents, the author falls into a well-known fallacy 

 in stating that " the maximum work is produced in the 

 depositing baths when their conductor resistance is equal 

 to the sum of the resistances of the source of supply 

 (dynamo) and conducting wires." A dynamo of reason- 

 able size would give its full output, absorbing only 10 

 or 15 per cent, of the total power internally, in which 

 case the apparent resistance of the baths would be 8 or 

 9 times that of the machine, and by decreasing this re- 

 sistance, to follow the author's rule, the dynamo would 

 be carrying about 5 times the load it was constructed 

 for, with results which can be imagined. Excepting, 

 however, a few slips of this kind which are not peculiar 

 to this work, we can certainly recommend this book as- 

 a practical guide to those engaged in any of the arts with, 

 which it deals. 



A Manual of Orchidaceous Plants cultivated under Glass 

 in Great Britain. Part III. Dendrobium, Bulbo- 

 phyllum, and Cirrhopetalum. Chelsea : James Veitch. 

 and Sons, Royal Exotic Nursery. 



The great genus Dendrobium possesses in the Eastern 

 Hemisphere a rank and a varied development corre- 

 sponding to those of Epidendrum in the Western Hemi- 

 sphere. Each comprises a large number of species, and 

 each displays the most gorgeous colouration. 



The former genus, Dendrobium, has now been ele- 

 vated to the rank of a sub-tribe, and includes the genera, 

 Aporum, Rhizobium, Cadetia, Sarcopodium, Strongyle,, 

 Stachyobium, and Eudendrobium, the last being the most 

 important. 



