Pyrheliometer

38S6

Pyromania

pus consists of an elevated membranous bor-
der, and the achcne? are angular but not
winded.

Pyrheliometer, an instrument, devised by
Pouillet to measure the heat radiated by the
sun. It consisted of a thin, dNc-shiipcd metal
box containing water, to act ;LS a calorimeter,

\vintcrgreen family, allied to tbe heaths, and
usually found in shady woods. The flowers
are five-parted, borne in racemes on tracted
snipes, and the leaves are in a tuft at the base
and are often evergreen.

Pyromania. An insanity dependent upon
hereditary or acquired constitutional tondi-

^VJMtf-

Left, Pvramid of ("ht'ops; Riuhl, The Third Pvramid.

supported by an axial tube containing a
thermometer.

Pyridinc, C,\Hr,N, a basic compound occur-
ring in coal tar and in the oil obtained by
the distillation of bones, from both of which
substances it may be separated by distillation
of the, basic portion. It is the parent sub-
stance of u law number of derivatives, in-
cluding some of the natural alkaloids, such as
nicotine and piperidine.

Pyrites, strictly speaking, is bisulphide of
iron, FeSii, and occurs very commonly as a
brassy mineral (sp. xr. 5), crystallizing in the
cubic system, Hwtted in air it burns, yielding
sulphur dioxide gas, and leaving a residue of
ferric oxide. This reaction is largely employed
to prepare sulphur dioxide for tlut sulphuric
acid industry,

PyrocatccKin, GJI^OH):!, is ortho-diliy-
droxy-btmene, It is formed \vben cat whin
and .similar bodies are distilled, and is prepar-
ed from the Ruaisicol, C«Hi(OH)(OCH»), oc-
curring in beech tar by heating with hydriodic
add,

PyrograHoI, or Pyro^allic Acid, (^ij-jt
(OH)aT Is a trihydroxy-bemcne obtained by
heating gallic acid.

Pyrography LH *thc decoration of wood by
partially burning or charring/ producing ef-
fects like those of dark-brown paint.

Pyrola* A genus of low perennials in the

lion, uith periodic manifestations. It resem-
ble*, dipsomania and kleptomania. At times

Pyrograpky*

the patient experiences an impulse, generally
Irresistible, to set ftrc to something, and en*