1872.] Technology. I1I 
according to Pliny, was prepared especially at Rhodes. As black pigments, 
various kinds of charcoal and soot were used by the ancients, the same as 
nowadays; while they dyed animal skins black with nutgalls and sulphate of 
iron. By their acquaintance with the use of various kinds of ochre, and by 
mixing these, either with each other in various proportions, or with black 
pigments, brown pigments of various shades were obtained. Under the name 
of Alexandria blue, the ancients (the author includes in that term the ancient 
Egyptians, as well as Greeks and Romans) largely used a pigment containing 
oxide of copper, and they also were acquainted with a pigment containing 
cobalt. Indigo was not unknown to them, but it was not used for dyeing, 
their blue-dyed fabrics being obtained by the use of pastel-wood, Isatis 
tinctoria. They used the following yellow pigments:—Ochre, massicot, 
orpiment, and realgar; the latter are poisonous, and do not cover well; the 
former are devoid of any brilliancy. As to the yellow dyes used by them 
nothing is positively known, but it seems that woad, saffron, and other native 
plants were employed. Referring to yellow pigments discovered by modern 
chemistry, Naples yellow (antimoniate of lead), mineral yellow (oxychloride of 
lead), and the chromium colours, discovered by Vauquelin (1797), cadmium 
yellow, discovered by Stromeyer (1817), are mentioned. Among the modern 
yellow dyes, purrhee and picric acid are enumerated. Vermillion, red 
ochres, and minium were known from a remote antiquity, though neither 
Greeks nor Romans were acquainted with the artificial preparation of vermil- 
lion, which has been known to the Chinese for a very lengthy series of 
centuries past. As to red dye-stuffs, there can be no doubt that madder was 
known and used not only for dyeing fabrics but also in the shape of so-called 
lake. Kermes, a dye-stuff little known in this country, but yet used in France, 
was known to and used by the ancients, being undoubtedly used in Egypt in 
the time of Moses. Among the green paints the ancients were only 
acquainted with some native green-coloured compounds of copper, and with 
the acetates of that metal; the number of green pigments discovered in modern 
times is very large and need not be here alluded to. Of purple dyes known to 
and used by the ancients, the celebrated Tyrian purple is here at length 
spoken of. Among the molluscs from which this dye was obtained is the 
Fanthina prolongata, yet found in the Mediterranean, and a very common 
object in that sea near Narbonne (in this very ancient city there were Tyrian 
purple dye-works at least 600 years B.C.), where in our days some experiments 
have been made by Dr. Lesson which really prove that the mollusc just 
named yields, though only in very small quantity, an exceedingly beautiful 
purple. Dr. Bancroft was also acquainted with this fact, and made several 
trials for the purpose of ascertaining whether this dye-stuff might be again 
industrially applied. 
A cheap mode of preparing pure dextrine is given by O. Ficinus. 500 parts 
of potato-starch are mixed with 1500 parts of cold distilled water and 8 parts 
of pure oxalic acid, and this mixture placed in a suitable vessel on a water- 
bath, and heated until a small sample tested with iodine solution does not 
produce the reaction of starch. When this is found to be the case the vessel 
is immediately removed from the water-bath, and the liquid neutralised with 
pure carbonate of lime. After having been left standing for a couple of days 
the liquor is filtered, and the clear filtrate evaporated upon a water-bath until 
the mass has become a paste; this is removed by a spatula, and, having been 
made into a thin cake, is placed upon paper and further dried in a warm 
place ; 220 parts of pure dextrine are thus obtained. 
Dr. F. Stolba gives the following direCtions for cleaning glass vessels wherein 
petroleum has been kept. Thin milk of lime, used for washing glass vessels 
wherein this liquid has been kept, forms with the petroleum an emulsion, and 
renders it possible to remove all traces, and, by the addition of a small quantity of 
chloride of lime toa second washing with milk of lime, even the smell is taken 
away so completely as to render the vessels fit for pouring and keeping beer 
therein ; if warm milk of lime be used, the operation, which otherwise takes 
considerable time for completion, is rendered shorter. 
