Collotype

“ Whilst the gelatine is setting, precautions against vibration must be taken else the plate will be spoilt.
When dry, the collotype plate is sensitive to light and moisture; its surface shows a more or less regular series of convolutions which resemble those of the outer surface of the human brain, although, of course, very much smaller. The character of the grain is very important, for if it be too fine it will not take up a sufficiency of ink, and, on the other hand, if too coarse it will yield coarse impressions. ”

“ A sumptuous series of 20 books on art, written by experts for collectors, superbly illustrated in photogravure, collotype, and colour. The technical side of the art is duly treated. The first volumes are—
Mezzotints. By Cyril Davenport. With 40 Plates in Photogravure.
Porcelain. By Edward Dillon. With 19 Plates in Colour, 20 in Collotype, and 5 in Photogravure.
Miniatures. By Dudley Heath. With 9 Plates in Colour, 15 in Collotype, and 15 in Photogravure.
Ivories. By A. Maskell. With 80 Plates in Collotype and Photogravure. ”

“ The chemistry of colloids has now assumed such importance that it may be considered as a separate branch of the science. It has its own technical journal and deals largely with the chemistry of organic products. All living matter is built up of colloids, and hæmoglobin, starch, proteins, rubber and milk are examples of colloidal substances or solutions. Among inorganic substances, many sulphides, silicic acid, and the amorphous hydroxides, like ferric hydroxide, frequently act as colloids. ”

“ Almost all the substances of which animal and vegetable bodies consist are colloids, and this is, at all events, partly the reason why animals and plants have such varied forms, which have no resemblance to the crystalline forms of the majority of mineral substances. The colloid solid substances in organisms—that is, in animals and plants—almost always contain water, and take most peculiar forms, of networks, of granules, of hairs, of mucous, shapeless masses, &c., which are quite different from the forms taken by crystalline substances. ”

“ And the first result of the researches upon colloids which should be emphasized is that there are in fact at least two kinds of dissolved or suspended substances retained by animal membranes, which differ so radically in their other properties that their inclusion in the same class is sure to lead to serious confusion, unless special pains be taken to discriminate between them. As types of these two classes of colloidal mixtures may be taken an aqueous solution of gelatine and one of colloidal arsenious sulphide. ”

“ But long before the critical point of a colloidal solution is reached the variation in the charge of the colloidal particles alters their physical properties. An increase in their charge has the same effect as if the viscosity of the liquid were increased.
The bulk of our protoplasm consists of colloidal material, and the physical manifestations of life, such as muscular contractions and protoplasmic motions, and the innervations, are due to changes of the condition of these colloidal solutions. ”

“ In the first place no one of those colloids which make up the mass of a living body, appears capable of carrying on vital changes by itself: it is always associated with other colloids. A portion of animal-tissue, however minute, almost always contains more than one form of protein-substance: different chemical modifications of albumen and gelatine are present together, as well as, probably, a soluble and insoluble modification of each; and there is usually more or less of fatty matter. ”

“ Into the mass of mingled colloids, mostly insoluble and where soluble of very low molecular mobility or diffusive power, we have constantly passing, crystalloids of high molecular mobility or diffusive power, that are capable of decomposing these complex colloids, or of facilitating decompositions otherwise caused; and from these complex colloids, when decomposed, there result other crystalloids (the two chief ones extremely simple and mobile, and the rest comparatively so) which diffuse away as rapidly as they are formed. ”

“ Collodion Process.—A great impetus was given to photography in 1850, on the introduction of collodion (q.v.) , a very convenient vehicle on account of the facility with which the plates are prepared, and also because it is a substance as a rule totally unaffected by silver nitrate, which is not the case with other organic substances. Thus albumen forms a definite silver compound, as do gelatin, starch and gum. ”

“ Graham named the solids formed by the setting or coagulation of these liquids hydrogels. Solutions of colloids in solvents such as water and alcohol seem to be divisible into two classes. Both mix with warm water in all proportions, and will solidify in certain conditions. One class, represented by gelatin, will redissolve on warming or diluting, while the other class, containing such substances as silica, albumen, and metallic, hydrosulphides, will solidify on heating or on the addition of electrolytes to form a solid “gel” which cannot be redissolved. ”

“ It is in the most general sense that protoplasm is “fluid.” As Graham said (of colloid matter in general) , “its softness partakes of fluidity, and enables the colloid to become a vehicle for liquid diffusion, like water itself264.” When we can deal with protoplasm in sufficient quantity we see it flow; particles move freely through it, air-bubbles and liquid droplets shew round or spherical within it; and we shall have much to say about other phenomena manifested by its own surface, which are those especially char­ac­ter­is­tic of liquids. ”

“ This water may be removed by drying, only to be re-absorbed on cooling, but if the heating temperature is excessive the structure of the colloids is destroyed. This colloid theory explains many of the facts noted by earlier investigators such as Aron, Bischof, Seger, Olschewsky, etc., but it is not entirely satisfactory, though Rohland (5) —to whom the present prominence of this theory in Europe is largely due—persistently [25] maintains the contrary. One great objection is the fact that no characteristic inorganic colloid substance has been isolated from pure clay. ”

“ After a consideration of all the terms, it would seem that "lyophilic" and "lyophobic," or more special derivatives, "hydrophobic" are the least objectionable terms, since most colloids answer to one of these designations. When our knowledge of colloids becomes exact enough to sharply differentiate between these two classes then we may find names for those systems which now seem to have properties which place them in neither of the above. ”

“ It is not until solid matter rises from the crystalline to the higher condition of the colloid, that it becomes capable of absorption, diffusion, and even of assimilation; that, in a word, it assumes relations to the external world which show that it possesses an individuality higher than the cyrstal, and is, in fact, endowed with many of the activities belonging to those masses of colloidal matter which biologists have agreed to call living. ”

“ Jarvis, “is invisible under the most powerful microscope. The molecule is larger, but defies the microscope. But, having gone thus far, science had to go further. The next larger mass after the molecule, is the colloid. A colloid is a formless substance classified as a slime. It never takes a definite form like the crystalline substances. Solutions of gold can be made in the two forms—there is a colloidal gold and a crystalline gold.”
A look of stupefaction was on the faces of the inspector, the coroner and all that vast throng in the courtroom. ”

“ It is distinctive, but the use of the expression "colloidal solution" is to be strongly condemned, since it is so evident that substances in the colloidal condition are not dissolved, in the strict sense of the term. Colloidal particles are in a condition midway between solution and mechanical suspension, and they are held in this peculiar state of dispersion by virtue of their surface energy, electrical charge, their kinetic energy as manifested by the Brownian movement, and the adsorbed ions of electrolytes which are essential to the stability of all colloids. ”

“ It has made modern photography [Pg 118] possible, for the film we use in the camera and moving picture projector consists of a gelatin coating on a pyroxylin backing. If collodion is forced through fine glass tubes instead of through a slit, it comes out a thread instead of a film. If the collodion jet is run into a vat of cold water the ether and alcohol dissolve; if it is run into a chamber of warm air they evaporate. The thread of nitrated cellulose may be rendered less inflammable by taking out the nitrate groups by treatment with ammonium or calcium sulfide. ”

“ It also teaches that colloidal matter, when exposed to certain conditions, presents the phenomena of life, and that it can be formed from crystalline matter, and thus that the prima materia of which these are diverse forms contains potentially all the multitudinous kinds of animal and vegetable existence. This theory moreover harmonizes well with the views here advocated, for just as crystalline matter builds itself, under suitable conditions, along certain definite lines, so analogously colloidal matter has its definite lines and directions of development. ”

“ Dead protoplasm, such as a coagulated blood clot, is an irreversible colloid consisting of a fixed network, the meshes of which contain the "sol." There is no evidence of internal structure in living protoplasm, and Hardy supposes that structure in dead protoplasm is produced by submortem or postmortem changes associated with coagulation. Whether the phase rule can be applied to colloids is still an open question bound up with the complex nature of bodies of which we know so little. ”

“ In both plants and animals, as will be pointed out in the following chapter, practically all the vital activities of the cell protoplasm are definite manifestations of colloidal phenomena. Enzymes perform their catalytic functions by reason of their colloidal form. Proteins exist in colloidal form and are the seat of all vital functions. The regulation of the passage of materials into and out of the cell is governed by minute changes in the electrolyte concentration, etc., which produce enormous changes in the colloidal character of the protoplasm. ”

“ Lastly, the great difference in diffusibility between colloids and crystalloids, makes possible in the tissues of organisms a specially rapid re-distribution of matter and motion; both because colloids, being easily permeable by crystalloids, can be chemically acted on throughout their whole masses, instead of only on their surfaces; and because the products of decomposition, being also crystalloids, can escape as fast as they are produced: leaving room for further transformations. ”

“ Accordingly, when the crystalloids pass out of solution, they form crystals or precipitates intimately blended with the colloids. Thus, for example, when uric acid crystallises out of urine it carries with it the colloidal pigments. On the other hand, if the colloids are precipitated, the solvent capacity of the solution being [153] consequently depreciated, the crystalloids are deposited in intimate relation with the colloids. ”

“ But the living cell grows in a totally different way, very much as a piece of glue swells up in water, by “imbibition,” or by interpenetration into and throughout its entire substance. The semifluid colloid mass takes up water, partly to combine chemically with its individual molecules267, partly by physical diffusion into the interstices between these molecules, and partly, as it would seem, in other ways; so that the entire phenomenon is a very complex and even an obscure one. ”

“ The matter of which a living organism is constituted consists essentially of certain solutions of crystalloids and colloids. To this we may add an osmotic membrane to contain the liquids, and a solid skeleton to support and protect them. Finally, it would seem that a colloid of one of the albuminoid groups is a necessary constituent of every living being.
We may say, then, that a living being is a transformer of energy and of matter, containing certain albuminoid substances, with an evolutionary form, the constitution of which is essentially liquid. ”

“ Repeated studies have shown that particles of the sizes between 5μμ and 250μμ in diameter, which are visible under the ultramicroscope, are sufficiently small to bring about the surface phenomena which are known as properties of colloidal solutions. Further, the ultramicroscope permits the observation of the growth, or disintegration, under various chemical reagents, of the individual colloidal particles, which appear as scintillating points in the field of the microscope; and the study of changes in relationships during gel-formation, peptization, etc. ”

“ It is extremely hard and extremely stable. Ascending to compounds of two, three, or more elements, we get substances which are more complex and less stable; and at last we arrive at combinations which involve many elements and are extremely complex. Among these latter substances are some, called colloids, which [78] are neither solid, like crystals, nor fluid, like liquids, but in an intermediate state, like jelly or the white of an egg, in which the molecules have great mobility and are at a considerable distance apart, so that water can penetrate their mass. ”

“ The collodion of some makers always acts in the manner you describe; and we have known it remedied by the addition of about one drachm of spirits of wine to the ounce of collodion. Spirits of wine also added to the nitrate bath—two drachms of spirits of wine to six ounces of the aqueous solution—is sometimes very beneficial. When collodion is inert, and the colour remains a pale milk and water blue after the immersion, a few drops of saturated solution of iodide of silver may be added, as it indicates a deficiency of the iodide. ”