April 28, 1882.J 



* KNOWLEDGE 



559 



fc:£U^^^^ 



ifttfrsf to tf)t etJitor. 



\Tht Editor dofM not hold himaelf retpontibU for the opinions ofhii correrpondent^. 

 M* cannot undfrtiikf to return manHscript* or to corretpond teith their vriters. Alt 

 eemmumiratioH* *houlJ be a« $hort as pottiblt, consUtenily tcHh full and clear rtate- 

 wuntsofthe tcriter't mfuninff.'] 



All Editor^'il comntunicatiota tkould he addreaed io the Editor o^ KxowtRDGB; 

 mU Susvtett communicatioHi to the Publisherr, at tht OJice, 7i, Qreat Queen- 

 street, W.C. 



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•,* All Utters to the Editor itill be Numbered. For convenience of reference^ 

 eorre»ponde*t$, when r^erring to any Iftter, trill oblige btf mentioning its number 

 mnd the page on vhtch it appears. 



AH Lett'eri or Queries to the Editor lehich require attention in the current issue of 

 ExowLBDOB.fAou/J reach the Publishing Office not later than the Saturdag preceding 

 ike day qf publication. __ 



(I.) Letters to have a chance of appearing must be concise; they must be drawn 

 np in the form adopted for letters nere, so that thev may Ro untouched to the 

 printers ; private communications, therefore, as we'll as queries, or repliea. to 

 queries (intended to appear as such) should be written on separate leaveff. 



(II.) Letters which (either because too ionp, or unsuitable, or dealing; with 

 matters which others ha%"e discussed, or for any other reason) cannot find place 

 here, will t-ither bebrieily referreti toin answers to correspondents, or acknowledged 

 in a column reserred for the purpose. 



" In knowledj;e, that man only i 



state of transition V 



than fixity of opinion." — Faraday. 



to be contemned and def^pKed who is not in a 

 r is there anything more adverse to accuracy 





.^^ .. mistake, bnt ^eat harm in making none. Show 

 mistakes, and I will show you a man who has done 



ftothinff." — JAehiq. 



*• God's Orthodoiy is Truth."— OaW<-^ Kingsley. 



©wx (CoiTfgponljfnce Columns^. 



DOES THE MIXTURE OF BLUE AND YELLOW MAKE 

 GREEN LIGHT? 



[388]— In Vol. I., page 538, of Knowledge, Mr. W. Benson 

 asserts that chloride of copper affords, before the " blowpipe," a 

 eea-green or verdigris light. The following equally eminent autho- 

 rities, on the other hand, maintain that this light is blue. (1) 

 Crookes : " Mitchell's Manual of Assaying," page 370, " Chloride 

 of copper alone colours the flame blue;" (2), Plattner, " Probir- 

 kunst mit dem Lothrohre," page 269, " The azure-blue flame of 

 chloride of copper ; " (3), Berzelius " On the Blon-pipe," Whitney's 

 translation, page 82, " Chloride of copper gives a beautiful blue 

 flume, inclining to purple ;" and at page 211, writing of atacamite, 

 "alone it tinges the flame intensely blue ; " (4), Fresenius, " Qual. 

 Anal., 1872," page 192, "Chloride of copper affords a fine blue- 

 coloured flame, inclining to purple;" (5), Elderhorst, " Man. Bl. 

 Anal.," page 5t>, "An intense azure-blue colour, owing to the 

 formation of chloride of copper;" (6), Landaner, "Man. Bl. 

 Anal., 1881," page 27, "Copper chloride gives a sky-blue flame- 

 colonr." Mr. \V. Benson's optical terminology seems to be derived 

 chiefly from Winsor & Newton's colour-box ; but if, by the expression 

 " a verdigris light," he moans a green light, I would ask where was 

 the necessity of mixing the sodium-j-eUow with copper chloride- 

 green, to make its llame green ? 



Similarly, the above authorities (except Mr. Benson) might be 

 cited to show that the blowjiipe pyrocone is also blue, not " sea- 

 green ; " and, indeed, I suppose that Mr. Benson, like everybody 

 else, has remarked that the sea, within 100 miles of a shelving 

 shore, is scarcely two consecutive days the same colour ; grey, 

 green,* yellow, mnd-colonr, &c., and more than 100 miles from 

 shore, generally bine. 



If by the name " ultramarine " he means lapis lazuli, 1 would 

 remind him that that mineral is by no means pure blue, as it contains 

 a considerable proportion of red, which makes it violetish blue. As 

 regards the "green beam" phenomenon, would it not have been 

 better for Mr. Benson to have taken a prism and lens, before he 

 took a pen in hand, to write about a matter which, by his o^vn ad- 

 mission, he does not understand ? As a matter of fact, my Venetian 

 blinds are white, not green ; and I tried this experiment oftenest in 

 a small room without any blind at all. 



London, W. W. A. Ross. 



• Green sea-water seems due to yellow rays, reflected from a 

 sandy bottom, shining through deep-sea-water, which is bine. 



SIS E. BECKETT'S INVENTION IN SCREWDRIVERS. 



[389] — Many long and hard-worked years have gone by since I 

 gave freely to my profession (that of a surgeon) a small invention 

 of my own, in the form of a gilded spiral spring for treatment and 

 cure of deeply-buiied abscesses. It was a tube formed by running 

 a soft metal wire over a mandril in a lathe, exactly resembling the 

 8|iiral springs of a bell-hangcr. This tube possessed a marvellous 

 flexibility and self-adjusting power when inserted in the exit 

 channel of such a sac of jiurulent matter or of putrefying blood as 

 wo not unfrequently meet with, and are at our wits' end to know- 

 how to empty. Not emptied, the patient has but a narrow shrift, 

 for jiya^mia begins out of this horrible bag of decomposition, and 

 the patient very quickly goes out of the world like a rushlight. 



A smart French surgeon conceived thelhappy thought that such 

 a bag of horrors might be drained, and thus began a new practice 

 in our art, called " abscess-drainage," with excellent results in some 

 cases. Uis tubes were, however, made of vulcanised (that is, 

 sulphuretted) caoutchouc ; and giving off a constant, but very 

 minute, ijuantity of sulphur, and of sulphur-laden gases, the tubes 

 did more harm than good. 



It then occurred to me to roll a little gilded wire round a knitting- 

 needle, and withdrawing the stem, there was left to me the prettiest 

 tube of close-siding coils of glittering wire. Try this, tlu»u reader, 

 and you wiir be as charmed as I. So inconceivably flexible and 

 ready to take any figvu-e you may bend it to is it, that it was but a 

 little step to reach its applicabilities, and to find them quite too 

 delightful. Immediately 1 found my fortunate moment. There lay 

 — and long had lain — on a beautiful couch, in a lovely bfed -chamber, 

 filled with the soft and scented summer air of a grand London 

 suburb, a man still young and full 'of life, but chained (under all 

 those luxurious belongings) by a worse than Promethean bondage — 

 an abscess, the sac of which lay half-a-foot from the nearest skin 

 Bui"face. The abscess was hopelessly sunk so low that no existing 

 device in surgery could tap that vile reservoir of matter so as to 

 drain it. My wire tubes at once reached the central receptacle, 

 and no words can express the relief obtained, or the admirable ease 

 with which the i-eservoir was emptied. 



Under the name of my wire "drainage-tubes," these toy-like 

 instruments caught the approbation of surgeons, and they are now in 

 general use. By Sir James Paget's commendation, I sent a case to 

 the late American President's surgeons, accompanied by his 

 approval for their excellent work, and they were, I believe, adopted 

 in that sorrowful instance. 



I have written all this oddly non-referable memorandum, because 

 I was sure it would interest some of yotu- readers, and being trans- 

 ferred into the immortal pages of Knowledge, never be again for- 

 gotten. 



Now for you, my excellent and much-adored old friend. Sir 

 Edmund. Why hide the head and shank of your imprisoned screw 

 (all screws ought to bo imprisoned, but not hidden) ? How can 

 you see with your metal straight-waistcoat over the head and tail of 

 your screw, which way the creature is tending— very likely to right 

 of you, or to left of you, or, by turns (of course), all around of yon ? 



This is the more excellent plan : — Make your guiding tube of 

 springy, well-tempered steel wire, w-ith the coils not too close to 

 each other. Thus, you can see your inward way ; the screwdriver 

 head slowly, but surely, thrusts its captive " home," and lightened 

 in its work, as in its self-clearing — you also — the great, wise, and 

 thoroughly typical Englishman of many sciences will gratefully 

 remember f — Your faithful, Robert Elus. 



TRICYCLES. 



[390]. — Would your correspondent, " Ex-Bicyclist," give us this 

 further information. Has he trieil the Omnicyclo ? And, if so, 

 where does he rank it in comparison with the five or six he 

 mentions ? A Woi ld-be Tricvclist. 



[We have received several letters for " Ex-Bicyclist," but we 

 have not his address, and we cannot undertake to forward letters to 

 correspondents. — Ed.] 



REPLIES TO QUERIES. 



[352]. — Add nitric acid (not too concentrated) to metallic copper. 

 3Cu + 4HO.N05 = 3CuO N0s-h4H0 + NOo.— F. G. A. 



[342] — Gold. — Pnt the gold-bedaubed paper into some nitro- 

 hydrochloric acid and heat gently in a glass beaker. Filter care- 

 fully and evaporate to dryness, taking care that the acid fumes do 

 not come into contact with an}-thing. The dry residue should be 

 heated, and will then be metallic gold. — P. G. A. 



No. 18, p. 376, col. 2— Spinning Top.— Will the Editor kindly give 

 the answer to these four questions, or say where I can find them 

 (the answers) ? — F. G. A. 



