Cooley's Cyclopaedia of Practical Receipts Volume Ii Part 113

This peculiar cracking in the paint is, according to Dr Liebreich, particularly observable in Guericault's 'Wreck of the Medusa' in the Louvre, and also in Ingres' 'Portrait of Cherubini,' and as the same defect is not to be seen in the works of the Dutch and Italian artists, the very rational inference to be drawn is that the methods followed by these schools were sounder than those adopted by their English and French successors. Dr Liebreich believes the cracks were owing to the practice of painting over one colour with another before the first was perfectly dry.

"The study of the alterations," says Dr Liebreich "already fully developed within the last hundred years only, and their comparison with the works of the old masters would suggest the following rules for the process of painting:--

"1. That the oil should in all colours be reduced to a minimum, and under no form should more of it than absolutely necessary be introduced into a picture.

"2. All transparent colours which dry very slowly should be ground, not with oil at all, but with a resinous vehicle.

"3. No colour should be put on any part of a picture which is not yet perfectly dry, and above all, never a quick-drying colour upon a slowly-drying one which is not yet perfectly dry.

"4. White and other quick-drying opaque colours may be put on thickly. On the contrary, transparent and slowly-drying colours should always be put on in thin layers. If the effect of a thick layer of these latter is required, it must be produced by laying one thin layer over another, taking care to have one completely dry before the next is laid on. If transparent colours are mixed with sufficient quant.i.ty of white lead they may be treated like opaque ones."

Dr Liebreich concludes his interesting lecture with some judicious advice on the subject of picture cleaning, and points out that, since different pictures require to be differently operated upon, all universal agents and methods suggested for the purpose are open to suspicion and should be discarded.

For pictures the varnish of which has become cracked or dim he recommends Pettenkofer's treatment with alcoholised vapour, already described. For those in which the varnish may have become dark yellow, brown, or dirty, he advises its removal altogether, being very careful to specify the conditions under which this should be accomplished, and the risk the picture may run of being spoiled if entrusted to an unintelligent and ignorant manufacturer. "If a picture," he says, "is throughout painted in oil, if its substance has remained sound and even, and it has been varnished with an easily soluble mastich or dammar varnish, there will be neither difficulty nor danger in removing the varnish. This can, in such a case, be done either by a dry process, that is by rubbing the surface with the tips of the fingers and thus reducing the varnish by degrees to a fine dust, or by dissolving the varnish by application of liquids which, when brought only for a short time into contact with the oil painting, will not endanger it. We have, however, seen that the works of the old masters are not painted with oil colours like those used by modern painters, but, on the contrary, that certain pigments, and especially the transparent colours used for glazing, were ground only with resinous substances. These latter have in the course of time been so thoroughly united with the layer of varnish spread over the surface of the picture that there no longer exists any decided limit between the picture and the varnish. It is in such pictures that a great amount of experience and knowledge of the process used for the picture, as well as precaution, are required, in order to take away from the varnish as much only as is indispensable, and without interfering with the picture itself.

"Numberless works of art have been irreparably injured by restorers, who, in their eagerness to remove dirt and varnish, attacked the painting itself. They then destroyed just that last finishing touch of the painting without which it is no longer a masterpiece."

"The cleaner is, then, reminded that if the removal from the pictures of their varnish, when this is known to consist of a spirituous solution of the gums mastich or dammar, requires the amount of discretion and judgment before specified, still greater care and prudence are necessary when dealing with pictures whose surfaces have been covered with oil, oil varnish, or oleo-resinous varnish. All these substances, which in time more or less obscure the picture, form on its face a dark and opaque film, and this frequently requires for its removal the application of some agent, which, in dissolving the layer of varnish, is very liable at the same time to dissolve the substance of the picture also."

As a recent instance of the injurious effects of injudicious picture cleaning, Dr. Liebreich mentions the case of a valuable picture in the Pitti Palace, at Florence, the 'St John of Andrea del Sarto.' The softness of the outline of the face of the figure, which he remembers previous to its attempted restoration, had been entirely destroyed, which disastrous result Dr Liebreich conceived had been caused by the entire removal of the glazing.

A new method for cleaning pictures is described by E. Von Bibra in the 'Journal fur Praktische Chemie.' A very indistinct oil-painting was freed from dust with a feather, washed with a sponge and water, and then covered for eight minutes with a layer of shaving soap. The soap was then washed off with a brush and then left to dry. It was next thoroughly cleaned with linen cloth soaked in nitro-benzol. The picture was now distinct, but the colours dull. Finally, it was treated with olive oil, and a coating of quick-drying varnish laid on. (Academy, May 6th, 1878.)[88]

[Footnote 88: In giving insertion to the above, we do not venture to give an opinion as to its value or the reverse. We would recommend it to be read side by side with Dr Liebreich's advice on picture cleaning, given above.--ED.]

=PAINTS.= In trade, this term is commonly applied to pigments ground with oil to a thick paste, ready to be 'thinned down' with oil or turpentine to a consistence adapted for application with a brush.

Paints are prepared on the small scale by grinding the dry pigments with the oil by means of a stone-and-muller; on the large scale they are ground in a colour mill. There are several pigments, as King's yellow, Scheele's green, verdigris, white lead, &c., which from their poisonous character cannot be safely ground by hand, except in very small quant.i.ties at a time, and then only by the exercise of extreme caution.

In mixing or thinning down paints for use it may be useful to mention that--for outdoor work, boiled oil is princ.i.p.ally or wholly employed, unless it be for the decorative parts of houses, when a portion of turpentine and pale linseed oil is often added.--For in-door work, linseed oil, turpentine, and a little 'driers,' are generally used in the same way. The smaller the proportion of oil employed for the purpose, the less will be the gloss, and the greater the ultimate hardness of the coating.

For 'flatted white,' &c., the colour being ground in oil, requires scarcely any further addition of that article, as the object is to have it 'dead' or dull. The best driers are ground litharge, and ground sugar of lead; the first for dark and middle tints, and the last for light ones.

To preserve mixed paints in pots from 'skinning over' or drying up, they should be kept constantly covered with water; or, what is better, with a thin film of linseed oil.

Brushes, when out of use, may be preserved in a similar manner to mixed paints. When dirty, or required for a paint of another colour, they may be cleaned with a little oil of turpentine, which may be either preserved for the same purpose another time, or may be allowed to deposit its colour, and then used to thin down paints as usual. In no case, however, should it be thrown back into the cistern or pan with the pure 'turps.'

=Paints, Flex'ible.= _Prep._ Take of good yellow soap (cut into slices), 2-1/2 lbs.; boiling water, 1-1/2 gall.; dissolve, and grind the solution whilst hot with good oil paint, 1-1/4 cwt. Used to paint canvas.

=Paints, Vitrifi'able.= See ENAMEL, GLAZE, STAINED GLa.s.s, &c.

=PALLA'DIUM.= Pd. A rare metal discovered by Dr Wollaston in the ore of platinum, in 1803.

_Prep._ 1. A solution of the ore of platinum in _aqua regia_, from which most of the metal has been precipitated by chloride of ammonium, is neutralised by carbonate of sodium, and then treated with a solution of cyanide of mercury; the white insoluble precipitate (cyanide of palladium) is next washed, dried, and heated to redness; the residuum of the ignition (spongy palladium) is then submitted to a gradually increased pressure, and welding at a white heat, so as to form a b.u.t.ton, in a similar manner to that adopted with platinum. _Prod._ Columbian ore of platinum, 1%; Uralian do., 25% to 75%.

2. The native alloy of gold and palladium (from the Brazils) is submitted to the operations of quartation and parting, the nitric acid employed being of the density of 13; the silver is next precipitated from the solution by means of a solution of common salt or dilute hydrochloric acid, and the decanted supernatant liquid, after evaporation to one half, is neutralised with ammonia, and concentrated so that crystals may form; these (chloride of palladium and ammonium) are cautiously washed in a little very cold water, dried, mixed with borax, and exposed in a crucible to the strongest heat of a powerful blast furnace, when a solid b.u.t.ton of pure palladium is formed.

_Prop., &c._ Palladium closely resembles platinum in appearance, fusibility, malleability, and ductility; but it is less dense, and has a rather more silvery colour than that metal; it is freely soluble in aqua regia, and is slowly attacked by nitric acid, but the other acids exert little or no action on it; heated to redness in the air, a very superficial blue or purple film of oxide forms on the surface, which is again reduced at a white heat. It melts at 156--Wedgwood. Sp. gr. 113 to 121 (118--Wollaston; 1214--Vauquelin). It readily unites with copper, silver, and some other metals, by fusion.

_Tests._ 1. The neutral solutions of palladium are precipitated in the metallic state by ferrous sulphate, dark brown by sulphuretted hydrogen, olive by ferrocyanide of pota.s.sium, and yellowish white by cyanide of mercury.--2. A drop of tincture of iodine placed on the surface of metallic palladium, and then evaporated by the heat of a spirit lamp, leaves a black spot. By the last two tests palladium is readily distinguished from platinum.

_Uses._ It has been employed to form the scales of mathematical and astronomical instruments, and is used in dentistry. Its alloy with silver is a very valuable white metal. It is also used for making the smaller divisions of grain and gramme weights. Palladium is not tarnished by sulphuretted hydrogen. An alloy of 1 part of palladium and 100 parts of steel is well adapted for cutting instruments which require to be perfectly smooth on the edge.

=PALMIT'IC ACID.= HC_{16}H_{31}O_{2}. Prepared from palmitin (_see_ next article), by saponification, as stearic acid is prepared from stearin. It forms pearly scales, and melts at 140 Fahr., like margaric acid, which it closely resembles.

=PAL'MITIN.= _Syn._ TRIPALMITIN. C_{3}H_{5} (C_{16}H_{31}O_{2})_{3}. The solid portion of palm oil, purified by crystallisation from hot ether.

White; soluble in ether and slightly so in hot alcohol; melts at 118 Fahr.; by saponification it is converted into palmitic acid. (See _above_.)

=PALPITA'TION.= _Syn._ PALPUS, PALPITATIO CORDIS, L. A violent and irregular beating or action of the heart, either temporary or occasional.

When it does not arise from sudden or violent agitation or distress of mind, it may be regarded as a symptom of a disturbance of the nervous functions by disease, in which case attention should be directed to the removal of the primary affection.

=PAL'SY.= See PARALYSIS.

=PANACE'A.= A term formerly applied to chose remedies which were supposed to be capable of curing all diseases, and still applied to some quack medicines.

=PANA'DA.= See BREAD JELLY (under JELLY).

=PAN'ARY FERMENTA'TION.= The vinous fermentation as developed in the dough of bread.

=PAN'CAKES.= These are essentially fried batter, variously enriched and flavoured, according to the taste of the cook. When they contain fruit, fish, meat, or poultry, or are highly seasoned or ornamented, they are commonly called FRITTERS.

_Prep._ (M. Soyer.) Break 2 to 4 eggs into a basin, add 4 small table-spoonfuls of flour, 2 teaspoonfuls of sugar, and a little salt; beat the whole well together, adding, by degrees, 1/2 pint of milk, or a little more or less, depending on the size of the eggs and the quality of the flour, so as to form a rather thick batter; next add a little ginger, cinnamon, or any other flavour at will; lastly, put them into the pan, and when set, and one side brownish, lay hold of the frying-pan at the extremity of the handle, give it a sudden but slight jerk upwards, and the cake will turn over on the other side; when this is brown, dish up with sifted sugar, and serve with lemon. See FRITTERS.

=PANCREAS.= This gland, popularly known as the sweet-bread, secretes a colourless and slightly viscid fluid, which possesses the properties of--1. Converting starch into sugar; 2. Of emulsifying fats and oils. And since it is necessary that the starchy and the fatty ingredients of the food should undergo this preparatory change before they are in a condition to become a.s.similated by the animal economy, it will be seen that _pancreatin_ (as the secretion from the pancreas is called) performs an important function in bodily nutrition.

With a knowledge of these facts before them, it is not surprising that the employment of pancreatin in disease should have been recommended by therapeutists. Dr Harley, we believe, first brought this remedy to the notice of medical men in 1858, since which time its princ.i.p.al advocate has been Dr Horace Dobell, whose method of preparing an emulsion from it, as well as for procuring the pancreatin pure and simple, are given below.

Bernard, correctly divining that the pancreatic fluid was concerned in the process of digestion, conceived that it aided the a.s.similation of the fatty and oily portions of the food, by saponifying them. Subsequent physiologists have, however, shown, "that the action of the pancreatic secretion is evidently to break up the large granules, crystals, and globules of oil and fat into myriads of minute particles of from 1/3000th to 1/15000th of an inch in diameter. In this way the fat is emulsified and converted into a milky liquid, which mixes freely with water, and pa.s.ses through the tissues of the intestines into the lacteals."[89]

[Footnote 89: Letheby.]

Pancreatin has an alkaline reaction, and putrefies very quickly. It seems to contain a nitrogenous organic principle, resembling ptyalin or diastase in properties. It is coagulated both by heat and nitric acid, and is one of the few secretions in which alb.u.men is present in a soluble condition.

Even when rendered acid, pancreatin does not lose its power of emulsifying fatty bodies. At the moment of food being introduced into the stomach the pancreas gives out this secretion, which is not very abundant at first, but gradually continues to increase for about four hours, when it as gradually diminishes for three hours more, and then ceases altogether.

Bidder and Schmidt give the following as the composition of the pancreatic fluid or pancreatin:--

Water 90076 Organic matter (pancreatin) 9038 Chloride of sodium 736 Free soda 032 Phosphate of soda 045 Sulphate of soda 010 Sulphate of pota.s.sa 002 {Lime 054 Combinations {Magnesia 005 {Oxide of iron 002 -------- 100000

=PANCREATIN.= _Syn._ PANCREATINUM. 1. (Pereira.) Cut the fresh pancreas of the pig, freed from fat and all foreign matters, into small pieces, and digest with ether. If the ether be afterwards distilled off from the filtered liquid, the pancreatin will be left as an oily product.

2. (Griffith.) It is obtained from the pancreas of recently killed animals by treating the colourless, viscous juice with alcohol, and drying the precipitate _in vacuo_. Pancreatin is given for stimulating the digestion of fatty compounds.

The ordinary dose is 10 grains, taken in a gla.s.s of wine or water after a meal.

Dr Dobell's "Crude Pancreatic Emulsion" is prepared as follows:--After freeing from fat and all foreign matters the pancreas of a freshly-killed pig, 2-1/2 lbs. of purified pancreas are bruised in a marble mortar, and to it are added 2-1/2 lbs. of lard; these are well beaten together, and then to the mixture 3 lbs. of water are added, very gradually, so as to ensure the perfect absorption of the latter.

The pancreatised fat is prepared by shaking up one part of the 'crude emulsion' with three parts of ether, allowing the mixture to stand, drawing off the ethereal solution, and carefully distilling off the ether.

The pancreatised fat remains. Dr Dobell says that pancreatised fat, unlike the crude fat, has no tendency to putrefy. His 'purified pancreatic emulsion' is made by mixing very carefully together 5 parts of pancreatised fat, 7-1/2 parts of distilled water, and 2-1/2 parts of rectified spirit, and flavouring with oil of cloves.