yune%, 1876] 



NATURE 



131 



dangerous mode (from the failure of any one of the delicate 

 manipulations introduced) for one analysis, will probably arrive 

 in the end, at a result more closely appro.iching to the truth. 



Blowpipe Assay of Ores, Furnace Products, &'c., for Cobalt. 



I. The rationale of this process depends upon the observa- 

 tions (a), that a trace (say '5 mgr.) of cobalt oxide affords, when 

 dissolved in a bead of microcosmic salt, the same colour (violetish 

 blue) which is afforded by the addition to a similar bead ol five 

 times as much oxide, or 2-5 mgrs. ; and {b) that these relative 

 quantities of cobalt oxide afford, when dissolved in phosphoric 

 acid beads of the same weight (say 60 mgrs.), perfectly different 

 colours ; v\z., pink as regards the smaller proportion, violet zs 

 regards the greater. 



3. The corollary derivable from these premises seemed to me, 

 therefore, that, the quantity of phosphoric acid being kept con- 

 stant, it would require the addition of more soda to turn the 

 pink bead than the violet bead blue; first, because violet already 

 contains blue, and fecond, because the cobalt might be presumed 

 to have already saturated, as a chemical base, part of the phos- 

 phoric acid. 



3. I was exactly wrong in this assumption. Different quantities 

 of soda were, indeed, required to azurise the two beads, but the 

 violet bead required more than the pink one, 



4. Without troubling the reader with ttdious details, I may 

 state here that each of three assays constantly showed the neces- 

 sity of an addition cf 14 mgrs. of fused sodium carbonate in 

 order to azurise a 60-mgrs. bead of phosphoric acid, made pink 

 by the solution in it of '5 mgr. of pure cobalt oxide ; and (by 

 three other assays) an addition of 20 mgrs. of soda to azurise a 

 60 mgrs. bead made violet by 3 '5 mgrs. of cobalt oxide. The 

 ratio, therefore, stood thus : — 



NaC 

 20 



NaC 

 14 



CoO 



3 '5 



CoO 



•5 



or the violet standard of cobalt was to the pink standard, as 

 2'4S : 071. It would, by these assays, seem that every half 

 milligramme between those extremes of cobalt oxide dissolved, 

 requires the addition to the bead of one milligramme of fused 

 sodium carbonate, in order to azurise a 60 mgrs. bead of pure 

 phosphoric acid. 



5. The way to operate is to compare, by reflected and trans- 

 mitted light, the blue colour thus obtained, with that of two 

 60 mgrs. beads of microcosmic salt, having the above-named 

 quantities of pure cobalt oxide respectively dissolved in them. 

 Space does not allow me here to describe the mechanical details 

 of operatic ns, which must be conducted with the utmost 

 care. 



6. From these facts, the following analytical table, as regards 

 ctbalt, is deduced : — 



CoO mgri. NaCos mgrs. 

 o*5 requires 14 = 083 



per cent, of a 60 mgrs. phosphoric 

 acid bead. 



The use of this table is shown in the following example : — 



7. Assay {for Cobalt only) of Smaltine, from a Freiberg 

 Cabinet. 



a. Weight of powdered ore crushed be- 

 tween agates = 



j3. Weight of powdered ore after roastirg 



on aluminium plate = 



Therefore the loss in arsenic and vola- 

 tile constituents = 



y. Weight of a new platinum wire with 

 a ring of I diameter 1 = 



5. Weight of the same platinum wire with 



a bead of phosphoric acid fused on it = 



6. Weight of the bead and wire after 



2*5 mgrs. of (i8) had been dissolved 



in the former = I24'0 



ipgrs. per cent. 

 50 - 

 18 56 

 32 

 71-5 

 134-5 



64 



This refers to the " ringing forceps." 



mgrs. per cent. 

 C. Weight of the bead and wire after 

 the addition of fresh phosphoric 



acidi = 132-5 — 



(This bead being rose colour,' fused sodium carbonate was 

 cautiously taken up from an agate slab and dissolved in it under 

 O.P.). 



7j. Weight of soda required to colour to 



the >/Mf of mic. salt with 2"5 CoO... = 16 "5 — 

 Now, by the above table (6), 16 '5 mgrs. oi soda correspond to 

 3 per cent, of a 60 mgrs. bead in pure CoO ; and 2*5 mgrs. of 

 pure CoO, requiring 18 mgrs. of soda, constitute 4'i per cent, 

 of the bead. Therefore we have the ratio — 



4" I : 3 :: 100 = |jths of 100 = 75 per cent. 

 But, as this is the percentage of the roasted powder, or " regulus,' 

 we have — 



Regulus Percentage Mgrs. 



in of regulus. of 



100 mgrs. mgrs. ore. 



36 : 75 : : 100 = 20*08 per cent, cobalt. 

 Several assays were made with a similar result, but one oiher 

 example is given here, with a different platinum wire. 



mgrs. 



a. Weight of a platinum wire = 610 



j8. ,, ditto with bead of phosphoric acid =1310 



7. ,, roasted smaltine dissolved in (/3). = 25 



8, ,, this wire with bead coloured rose 



pink with (7) = Ii8'5 



c. ,, bead and wire with fresh phos- 

 phoric acid = 1210 



f. ,, sodium carbonate required to 



colour (e) 3/?<(f = 165 



8. These data would, of course, give a similar result Roast- 

 ing before O. P. on aluminium plate is so rapid ana efficacious 

 that the whole process only occupies about half an hour ; with 

 the roasted powder, about a quarter of an hour. A drop of water 

 is placed on the powder to retain it under the blast 



In roasting, nickel oxide appears, yellowish green, on the sur- 

 face, and might possibly be mechardcally separated at this stage 

 of the procedure. W. A. R( ss 



Page's Introductory Text-book of Physical Geography 

 It has been pointed out to me that the same errors which I 

 noted in this book (Nati'RE, vol. xiv. p. 26). had betn 

 corrected as regards Prof. P ge's "Advanced Text-book " by 

 Mr. Wallace three years ago. 'J'hey can scarcely, therefore, be 

 anything but wilful, and it is difficult to understand how they 

 could be allowed to leappear. We do expect teachers of posi- 

 tion at least to do their best to teach rightly ; and when one 

 has fallen into error it is certainly more manly to correct it than 

 to stick to it, because it has once been cf mmitted. It is a good 

 thing to teach science, but it is just the opposite deliberately to 

 teach false science. The Reviewer 



OUR ASTRONOMICAL COLUMN 



The Secondary Light of Venus.— By way of sup- 

 plement to the historical notes on the luminosity of the 

 " dark side " of the planet Venus in last week's " Astro- 

 nomical Column," a brief enumeration of the various 

 explanations of the phenomenon which have been offered 

 from time to time may not be out of place here. 



These resolve themselves into (i) reflected earth-light 

 analogous to the lumi^re-cendr^e exhibited by our moon, 

 an explanation advanced by Schroter, Harding, and many 

 others ; (2) phosphorescence of the planet's atmosphere, 

 suggested by Sir W. Herschel to account for the appear- 

 ances remarked by Schioter, though looked for without 

 success by himself, with which may be mentioned Pas- 

 torflf 's idea of a self-luminous atmosphere ; (3) visibility 

 by contrast — "might not a plausible explanation be 

 given," asks Arago, " by referring it to a class of objects 

 which are negatively visible, or which are rendered 

 apparent by way of contrast ?" (4) luminosity, similar to 

 our polar-light (aurora borealis) ; (5) natural light-deve- 

 lopments, as luminosity of the ocean ; (6) a condition of 



» This is necessary to make up the weight of the bead to 60 mgrs. After 

 the addition of soda, thtre is no loss from volatilisation. 

 * From the interference of iron and nickel oxides in the assay. 



