BLU 
properties of albumen. When heated, a 
brown-coloured scum gathers on its surface. 
If it be evaporated to dryness, and then 
mixed with alcohol, a portion is dissolved, 
and the alcoholic solution yields by evapo- 
ration a residuum, which lathers like soap 
in water, and tinges vegetable blues green ; 
the acids occasion a precipitate from its so- 
lution. This substance is a compound of 
albumen and soda. Thus we see that the 
watery solution contains albumen, iron, and 
soda. When new-drawn blood is stirred 
briskly round with a stick or the hand, the 
whole of the fibrin collects together upon 
the stick, and in this manner may be sepa- 
rated altogether from the rest of the blood. 
The red globules in this case remain behind 
in the serum. It is in this manner that the 
blood is prepared for the different purposes 
to which it is put ; as clarifying sugar, mak- 
ing puddings, &c. After the fibrin is thus 
separated, the blood no longer coagulates 
when allowed to remain at rest, but a 
spongy flaky matter separates from it, and 
swims on the surface. 
BLUE, otherwise called azure, is one of 
the primitive colours of the rays of light. 
Blue, painters, is made different accord- 
ing to the different kinds of painting. 
In limning, fresco, and mi mature, they use 
indifferently ultramarine, blue ashes, and 
smalt : these are their natural blues, except- 
ing the last, which is partly natural and 
partly artificial. 
In oil and miniature they also use indigo 
prepared ; as also a fictitious Ultramarine. 5 
Enamellers and painters upon glass have 
blues prpper to themselves, each preparing 
them after their own manner. s 
BLUING of iron, a method of beautify- 
ing that metal sometimes practised ; as for 
mourning buckles, swords, or the like. The 
manner is thus ; take a piece of grindstone 
and whetstone, and rub hard on the work 
to take off the black scurf from it ; then 
heat it in the fire, and as it grows hot the 
colour changes by degrees, coming first to 
a light, then to a dark gold colour, and' lastly 
to a blue. Sometimes they grind also indi- 
go and sallad oil together, and rub the 
mixture on the work with a woollen 
rag while it is heating, leaving it to cool of 
itself. Among sculptors we also find men- 
tion of bluing a figure of bronze, by which 
is meant the heating of it to prepare it for 
tiie application of gold leaf, because of the 
bluish cast it acquires in the operation. 
BLUENESS, that quality which denomi- 
nates a body blue, depending on such a size 
BLU 
and texture of the parts that compose the 
surface of a body, as dispose them to reflect 
the blue or azure rays of light, and those 
only, to the eye. 
With respect to the blueness of the sky, 
M. de la Hire, after Leonardo da Vinci, ob- 
serves, that any black body, viewed through 
a thin white one, gives the sensation of 
blue; and this he assigns as the reason of the 
blueness of the sky, the immense depth of 
which, being wholly devoid of light, is view- 
ed through the air illuminated and whiten- 
ed by the sun. For the same reason, he 
adds, it is, that soot mixed wdth white 
makes a blue; for white bodies, being al- 
ways a little transparent, and mixing them- 
selves with a black behind, give the per- 
ception of blue. From the same principle 
he accoimts for the blueness of the veins on 
the surface of the skin, though the blood 
tuey are filled with be a deep red ; for red, 
he observes, unless viewed in a clear, strong 
light, appears a dark brown, bordering on 
black : being then in a kind of obscurity 
in the vei »s, it must have the effect of a 
black ; and this, view r ed through the mem- 
brane of the vein and the white skin, will 
produce the perception of blueness. 
In the same way did many of the early 
writers account for the phenomenon of a 
blue sky ; but, in the explanation of this 
phenomenon, Sir Isaac Newton observes, 
that all the vapours, when they begin to. 
condense and coalesce into natural parti- 
cles, become first of such a bigness as to 
reflect the azure rays, before they can con- 
stitute clouds of any other colour. This, 
therefore, being the first colour which they 
begin to reflect, must be that of the finest 
and most transparent skies, in which the va- 
pours are not arrived to a grossness suffi- 
cient to reflect other colours. 
M. Bouguer, without having recourse to 
the vapours diffused through the atmo- 
sphere, in order to account for the reflec- 
tion of the blue-making rays, ascribes it to 
the constitution of the air itself, whereby 
these fainter-coloured rays are incapable of 
making their way through any considerable 
tract of it : and he accounts for those blue 
shadows, which were , first observed by 
M. Buffon in the year 1742, by the aerial 
colour of the atmosphere, which enlightens 
these shadows, and in which the blue rays 
prevail ; whilst the red rays are not reflect- 
ed so soon, but pass on to the remoter re- 
gions of the atmosphere. 
The Abbe Mazeas, in a Memoir of the 
* 0CIet y in Berlin, for the year 1752, ac- 
- *v-v<ar'- 
