|
The stunted growth of the portion of the plant under the coloured Glass
was, no doubt, owing to the colour being too dense, and thereby excluding
too much light.*
The ancients were acquainted with the use
of the following metals for tinting Glass, as the analysis of various
specimens of Roman and Grecian fragments prove—viz., copper,
manganese, and iron; the latter, employed in different proportions and
admixtures with other metals, produced a beautiful azure blue, nearly
equal to the rich modern cobalt colour. See plate 2,
and the following table of analysis by Klaproth:—
| Red Glass. |
| Blue. |
| Green. |
| Sand |
162 |
163 |
130 |
| Oxide of Lead, Blaoxide |
28 |
— |
15 |
| Oxide of Copper |
15 |
1 |
20 |
| Iron oxide |
5 |
19 |
7 |
| Alumine |
2 |
3 |
11 |
| Kalkerede, Lime |
3 |
½ |
13 |
|
195 |
186 |
196 |
| Loss |
5 |
14 |
4 |
|
200 |
200 |
200 |
The above red and green Glasses are chiefly
coloured by
* A very light green is found
to answer better than a colourless glass for conservatories; and, by
recommendation of Mr. Hunt, author of "Researches on Light," &c.,
the new conservatories of the Royal Gardens at Kew have been glazed with
this description of flat Glass, in order to afford the plants protection
against the scorching heat of the meridian sun. A great improvement would
be effected by the panes being of an arched form, and placed in such
an aspect that the morning and evening rays of the sun would not have
a tendency to reflect the rays back again, as is the case with thick
flat Glass, in which, when the rays pass through it at right angles,
parts of irregular substance act as burning-glasses; whereas, by the
above arrangement, the rays would pass in a direct course through the
glass; and within, the condensed drip would be effectually carried off
by channels on each side of the interior of the frames.
|
