SCIENTIFIC SUMMARY. 
319 
well^ being quite equal to tbe grits and sandstones already so much used. — 
Vide The Artisan. 
Coal from Sea-ioced. — Some time since, says the Annales du Genie Civil, 
tbe practice was introduced of converting marine algce by calcination into 
an excellent coal superior to ordinary wood charcoal for filtering water, dis- 
infecting sinks, polishing glass and correcting the acidity and decolorising 
wines, — also for precipitating and decolorising vegetable alkaloids. Until 
recently no value was attributed to the marine algae — to-day they are an 
important article of commerce in several islands. 
The colours seen in tempering Steel . — An article in one of the American 
journals on the tempering of steel, states that the process is guided by the 
colour, and gives the following summary of the tints observed : — 1. Being 
put upon burning fuel, the steel gradually heated becomes tarnished, yellow, 
and straw-yellow. 2. The heat increasing, the colour deepens, and reaches 
a gold yellow, full yellow. 3. Afterwards, the steel takes several shades, 
rapidly following and blending with each other ; they are purple, pigeon’s 
throat, copper, brown yellow. 4. These shades become deeper until they 
become violet. 5. Afterwards they pass rapidly to indigo blue, full blue, dark 
blue. 6 . This colour becomes weaker, and gives a sky-blue more or less 
pure. 7. The blue takes a greenish tint and produces shades which are 
grey and sea-green. 8. At last the steel reddens, and will no longer give 
distinct colours. The shades of these eight colours, which are called tem- 
pering colours, are perfectly distinct, very apparent, and easy to recognise ; 
but they take place only after hardening and on clean steel. The metal 
which has not been hardened will not show these colours so plainly j the 
shades are mingled, blended, and less in number. — Vide Van Nostrand's 
Engineering Magazine, No. III. 
Failure of a proposed Flan for Armour Plates . — Armour plates, made by 
coiling bars of iron as for Armstrong gun tubes, welding the coil by upset- 
ting, cutting the coil in two, and flattening out the halves into plates, have, 
says one of the metallurgical journals, proved a great failure, as the experts 
prophesied. The welds were found very defective. 
IIoiv to Weld Copper. — The difficulty of welding copper due to the for- 
mation of an infusible oxide, has been, says the Mining Journal, overcome by 
a device of Mr. P. Bust, Inspector of Salt Mines in Bavaria. The use of 
microcosmic salt on the surfaces to be united succeeded perfectly, but was 
too expensive ; he, therefore, substituted a mixture of one part of the salt 
with two parts of boracic acid, which answered the same purpose as the 
original compound, with the exception that the slag formed was not quite 
as fusible as before. This welding powder should be strewn on the surface 
of the copper at a red heat j the pieces should then be heated up to a full 
cherry-red or yellow heat, and brought immediatel}'- under the hammer, 
when they may be as readily welded as iron itself. For instance, it is 
possible to weld together a small rod of copper which has been broken j the 
ends should be bevelled, laid on one another, seized by a pair of tongs, and 
placed together with the latter in the fire and heated ; the welding powder 
should then be strewn on the ends, which, after a further heating, may be 
welded so soundly as to bend and stretch as if they had never been broken. 
Mr. Bust has welded strips of copper plate, and drawn them into a rod 
VOL. YIII. — NO. XXXII. Y 
