FLAVOURED ICE-CREAMS are made by mixing cream for icing with half its
weight of mashed or preserved fruit, previously rubbed through a clean
hair sieve; or, when the flavour depends on the juice of fruit or on
essential oil, by adding a sufficient quantity of such substances.
RASPBERRY and STRAWBERRY ICES are made according to the former method;
LEMON, ORANGE, NOYEAU, and ALMOND ICES, by the latter method. In the same
way any other article besides cream may be frozen.
CHOCOLATE FOR ICING is made by rubbing 1 oz. of chocolate to a paste with
a tablespoonful of hot milk, and then adding 'cream for icing,' 1 pint.
COFFEE FOR ICING is made of cream for icing, 1 quart, to which a small
teacupful of the strongest possible clarified coffee has been added
together with 2 oz. of sugar and the yolks of 3 or 4 eggs. See ICING
(_below_).
=I'CING.= (For cakes.) _Syn._ SUGAR ICE. The covering of concreted sugar
with which the confectioners adorn their cakes. _Prep._ Beat the white of
eggs to a full froth, with a little rose or orange-flower water; then add
gradually, as much finely powdered sugar as will make it thick enough,
beating it well all the time. For use, dust the cakes over with flour,
then gently rub it off, lay on the icing with a flat knife, stick on the
ornaments while it is wet, and place it in the oven for a few minutes to
harden, but not long enough to discolour it. It may be tinged of various
shades by the addition of the proper 'stains.'
=ID'RIALIN.= A fusible, inflammable substance, found associated with the
native cinnabar of the mines of Idria, in Carniola. It is extracted from
the ore by means of oil of turpentine. It is only slightly soluble in
alcohol and ether. When pure, it is white and crystalline.
=ID'RYL.= A hydrocarbon generally found associated with idrialin.
=IGASU'RIC ACID.= _Syn._ ACIDUM IGASURICUM, L. An acid associated with
strychnine in the St. Ignatius' bean and in nux vomica. It may be obtained
by digesting the rasped or ground beans first in ether and then in boiling
alcohol, evaporating the latter decoction to dryness, diffusing the
residuum through water, adding a little carbonate of magnesium, again
boiling for some minutes, filtering, washing the powder with cold water,
and digesting it in alcohol, and filtering. The igasurate of magnesium
thus obtained is dissolved in boiling water, the solution decomposed by
acetate of lead, and the precipitate (igasurate of lead), after being
washed and diffused through distilled water, is decomposed by sulphuretted
hydrogen. The solution thus obtained yields crystals (igasuric acid) on
being evaporated. It is soluble in both water and alcohol.
=IGNI''TION.= In the laboratory this term is commonly applied to the act
of heating to redness or luminousness. See CALCINATION.
=ILLICIN.= Boil a clear decoction of holly with animal charcoal; let it
settle, collect the deposited charcoal, wash it with cold water, dry it,
and treat it with boiling alcohol; let the filtered liquid be evaporated
to dryness. Febrifuge.--_Dose_, 6 to 24 gr.
=ILLUMINA'TION.= The act of illuminating or making luminous. For supplying
artificial light to streets and the interiors of houses coal gas and oils
and fats are generally employed. These illuminating agents are compounds
rich in carbon, upon the presence of which the brightness of their flames
depends. Flame is gas or vapour heated to incandescence during the
process of combustion. A flame containing no solid particles emits but a
feeble light, even if its temperature is the highest possible. Pure
hydrogen, for instance, burns with a pale, smokeless flame, though with
the production of considerable heat. On the other hand, wax, paraffin,
coal-gas, &c., while undergoing combustion, give out considerable light,
because their flames contain innumerable solid particles of carbon, which
act as radiant points. To give the greatest degree of luminosity to flame,
the supply of air must be proportioned to the character of the burning
substance, and be insufficient for the instantaneous combustion of the
evolved gases; in which case the hydrogen takes all the oxygen, and the
larger portion of the carbon is precipitated, and burnt in the solid form,
at some little distance within the outer surface of the flame. When the
supply of air is sufficient for the immediate and complete combustion of
the whole of the combustible matter, no such precipitation takes place,
and the flame is neither white nor brilliant. The richest coal-gas, mixed
with sufficient air to convert all its hydrogen and carbon into water and
carbonic acid, explodes with a pale blue flash; yet the same gas, when
consumed in the ordinary way, burns with a rich white flame. Every one
must have noticed the effect of a gust of wind upon the flaring gas-jets
of a butcher's shop; the plentiful supply of air causes complete
combustion, and so converts the bright white flames into dull blue streaks
of fire. When the supply of air is insufficient to cause the combustion of
the newly formed solid carbon at the instant of its development, and
whilst it is in an incandescent state, the flame becomes red and smoky,
and unburnt sooty particles are thrown off. The same occurs when the
temperature of any portion of the hydrogen is reduced below that intensity
required for the combustion of the newly separated charcoal. Solid bodies,
as tallow, oils, and fats, which burn with flame, are converted into the
state of gas by the heat required to kindle them, and it is this gaseous
matter which suffers combustion, and not the substance which produces it.
The relative value of the ordinary illuminating agents has been accurately
determined by Dr Frankland. According to his experiments, the quantities
of various substances required to give the same amount of light as would
be obtained from 1 gallon of Young's Paraffin oil are as follows:--
Young's Paraffin oil 1·00 gall.
American rock oil[352] 1·26 "
Paraffin candles 18·6 lbs.
Sperm 22·9 "
Wax 26·4 "
Stearic 27·6 "
Composite 29·5 "
Tallow 39·0 "
[Footnote 352: Acknowledged to be an inferior sample.]
The following table exhibits the comparative cost of the light of 20 sperm
candles, each burning 10 hours at the rate of 120 gr. per hour; also the
amount of carbonic acid produced and heat evolved per hour, in obtaining
this quantity of light:--
Carb. acid Units of
Cost. per hour in heat
_s._ _d._ cub. feet per hour.
Wax 7 2-1/2 }
Spermaceti 6 8 } 8·3 82
Paraffin candles 3 10 6·7 66
Tallow 2 8 10·1 100
Rock oil 0 7-1/2 }
Paraffin oil 0 6 } 3·0 29
Coal gas 0 4-1/2 5·0 47
Cannel gas 0 3 4·0 32
These figures prove that coal-gas and the mineral oils are the cheapest
and best illuminating agents, producing the largest amount of light with
the least development of heat.
The light emitted by incandescent lime (DRUMMOND LIGHT, HYDRO-OXYGEN
LIGHT, LIME LIGHT, OXYHYDROGEN LIGHT) is intensely brilliant, and is often
made use of to enable workmen to continue operations at night. It is
obtained by directing the flame produced by the combustion of a mixture of
hydrogen (or coal-gas) and oxygen upon a small cylinder of lime. In the
improved form of this light the lime is protected from crumbling by a cage
of platinum wire, and is caused to rotate slowly by means of clockwork, so
as constantly to expose a fresh surface to the flame. When reflected from
a 'parabolic mirror' in a pencil of parallel rays, the Drummond light has
been recognised during daylight at a distance of 108 miles. The lime light
produced with coal-gas and oxygen is used for the MAGIC LANTERN and GAS
MICROSCOPE.
The most powerful illuminator is the ELECTRIC LIGHT, which is now being
subjected to trial in many cities for street illuminations, &c., in place
of coal-gas. It is usually produced by the passage of a strong current of
electricity between two pencils of hard carbon. The electric light has
been successfully applied to lighthouse illumination. Hitherto it has been
found too intense and too costly for application to domestic purposes. See
CANDLES, FLAME, GAS, PHOTOMETRY, &c.
=ILLU'TATION.= See BATH (Mud).
=IMAGINA'TION.= The influence of the imagination, both in the production
and cure of disease, has been long admitted by medical practitioners. It
is probably the most powerful therapeutic agent known. "Extraordinary
cures have been ascribed to inert and useless means, when, in fact, they
were referable to the influence of the imagination." (Dr Pereira.)
=IMPE'RIAL.= _Syn._ POTUS IMPERIALIS, PTISANA I., L. _Prep._ 1. Cream of
tartar, 1/4 oz.; 1 lemon, sliced; lump sugar, 2 oz.; boiling water, 1
quart; infuse, with occasional stirring until cold, then pour off the
clear portion for use.