In medicine, a fracture is the breaking of a bone. It is simple when the bone only is divided; compound when there is also a wound of the soft parts leading down to the fracture.
A fracture is termed transverse, longitudinal, or oblique according to its direction in regard to the axis of the bone.
It is called complicated if accompanied with dislocation, severe contusions, wounded bloodvessels, or any disease which prevents the union of the bones and causes them to be very easily broken.
A comminuted fracture is one in which the bone is broken into several small pieces at the point of rupture.
An incomplete fracture is one in which only a portion of the fibres is broken.
A stellate fracture is a series of fractures radiating from a centre.
When a fracture takes place there is a pouring out of fluid - lymph - and cells from the blood contained in the vessels of the lining membrane of the bone as well as from the vessels of the soft parts which have also suffered injury. This material surrounds the broken ends of the bone, becomes firm and consolidated, and in about three weeks is hard enough to keep the broken ends in position. A formation of bone then takes place round the seat of fracture. This is called 'provisional callus', because, when the process of repair is completed and true bone has formed to unite the break, it is re-absorbed and gradually disappears. Meanwhile a process of repair goes on between the broken ends, uniting them by the formation of true bone or 'definitive callus'. The more quickly and accurately after the break the broken ends are brought together, the more rapid will be the reunion. The treatment of a simple fractured bone is to bring the portions into their natural position and to keep them permanently thus, formerly by splints of some kind, pasteboard splints, for instance, dipped in warm water, with wooden ones exterior to them; or, as more recently, a mass of plaster of Paris may be used for the same purpose. Research Fracture
Casting (founding) is the process of producing solid objects by pouring molten material into a shaped mould and allowing it to cool.
Casting is used to shape such materials as glass and plastics, as well as metals and alloys. The casting of metals has been practiced for more than 6,000 years, using first copper and bronze, then iron.
The traditional method of casting metal is sand casting. The foundry floor was composed for several feet deep of a loamy sand, in which deep pits were some times sunk to buty large moulds. A wooden pattern of the object to be cast having been made, was pressed firmly down into this loamy sand, the sand being shovelled up all around, level with the top of the pattern and well rammed down. The pattern was then lifted out of the sand, and any small pieces of sand which may have fallen into the mould were carefully blown away, and some finely-powdered charcoal sifted over the surface. The molten metal was then poured into the mould until it was full. The whole was then covered with sand to keep the air from it while it cools. An open horizontal bed of sand was sufficient for casting many articles, but with articles of a more complex form and not too large, a frame or box, called a flask was generally employed to hold together the sand used in the casting, the number of flasks varying according to the form and parts of thee mould.
In ordinary operations the pattern was laid on a board known as the turn-over board, and the flask placed over it, the sand being carefully rammed into the flask until it was full. Another board, known as the bottom-board, was then laid upon it. The flask was then turned over, the first or turn-over board taken off, the one side of the pattern uncovered, a fine facing of sand spread upon the surface to prevent adhesion, after which a second flask, called the cope, sometimes made with crossbars to strengthen it and help to hold the sand, was placed upon it and sand carefully rammed in. The cope or second flask was then lifted off, the sand which it contains carrying the impression of the upper side of the pattern; the pattern in the lower part of the flask, or drag, was then carefully drawn out, and any injuries which the mould receives during the operation repaired. Holes or passages were then cut into the sand for pouring in the metal, all loose sand carefully removed, the cope replaced and secured to the drag by clamps. The mould was then ready for the molten metal. In pouring, the metal was generally run through two or three different passages at the same time to prevent it losing fluidity by cooling. It was only in lighter castings that sand, of the proper degree of dryness, porosity, and adhesiveness, was used.
In heavy castings the mould was usually made of loam, which is more adhesive, and in complicated articles the making of the mould was often a difficult process. Small articles of simple form and of easily-fusible alloys, such as bullets, printing types, etc, were often cast in metal moulds. Articles of sculpture were usually cast in plaster of Paris, which, when mixed with water, runs into the finest lines of a mould and takes a most exact impression. The variety of articles made by casting was very great: boilers, cisterns, cylinders, pumps, railings, grates, cannon, cooking-utensils, and many objects of decorative art.
Permanent metal moulds called dies are also used for casting, in particular, small items in mass-production processes where molten metal is injected under pressure into cooled dies. Continuous casting is a method of shaping bars and slabs that involves pouring molten metal into a hollow, water-cooled mould of the desired cross section. Research Casting
Dentl plaster is an unmodified hemi-hydrate gypsum plaster similar to plaster of Paris, but much more finely ground and generally produced from pure gypsum to produce a very good white colour. Dental plaster is generally used for dental surgery, but is also used in the paining and decorating trade. Research Dental Plaster
Diffusion is the gradual mixing of gases or liquids when brought into direct contact. Thus, in the case of gases, when a jar of oxygen and a jar of hydrogen are connected together by a tube or opening of any kind, they rapidly become mixed; and their mixture does not depend on gravity, but takes place in opposition to that force, as may be shown by placing the jar of hydrogen gas above the other. Oxygen is sixteen times heavier than hydrogen, bulk for bulk, but the heavier gas moves upwards and the lighter downwards, and the process of intermixture, or diffusion, goes on until the two gases are apparently equably distributed throughout the whole space. After that they have no tendency whatever to separate.
Similarly, if two vessels, one containing oxygen and the other hydrogen, be connected by a tube which is stuffed with a plug of porous material, such as plaster of Paris, the gases gradually diffuse one into the other through the porous plug. The two gases, however, do not pass through the porous separator at equal rates, but in inverse proportion to the square roots of the densities of the gases. Thus in the case of two vessels, one containing hydrogen and the other oxygen, which is sixteen times as heavy as hydrogen, the hydrogen will pass towards the oxygen jar four times as quickly as the oxygen will pass towards the hydrogen jar.
Kindred phenomena occur when two liquids that are capable of mixing, such as alcohol and water, are put in contact, the two gradually diffusing one into the other in spite of the action of gravity. In some cases, however, as where ether and water are employed, the diffusion is only partial, this result arising from the fact that these two liquids are not miscible in all proportions. When solutions of various solid bodies are placed in contact, interdiffusion also takes place. On the results of his examination of the phenomena of diffusion of liquids and salts across porous membranes or septa, Graham founded a method of separating colloid from crystalloid bodies, which he called dialysis. Research Diffusion
Plaster of paris is a form of hemhydrate plaster derived from rock gypsum crushed and heated to a temperature of 170 degrees celsius. This process removes some 75 percent of the water in the plaster, which when mixed with water sets (hydrates) very quickly. Research Plaster of Paris
Gypsum is a common monoclinic mineral distributed in sedimentary rocks, often as thick beds. Gypsum is usually found under beds of rock salt as it's one of the first minerals to crystallize from evaporated saltwaters and is also produced in volcanic areas and in rock veins due to the action of sulphuric acid. Gypsum is used in the production of plaster of Paris. It is chemically a hydrated calcic sulphate and has the formulae CaSO4.2H2O and a relative hardness of 2.
Gypsum is found in a compact state as alabaster, or crystallized as selenite, or in the form of a soft chalky stone, which in a very moderate heat gives out its water of crystallization, and becomes a very fine white powder, extensively used under the name of plaster of Paris. This last is the most common, and is found in great masses near Paris, where it forms the hill of Montmartre, near Aix in Provence, and near Burgos in Spain.
Gypsum may be geologically of any age, but occurs abundantly in the more recent sedimentary formations, and is even now forming, either as a deposit from water holding it in solution, or from the decomposition of iron pyrites when the sulphuric acid combines with lime, or from the action of, sulphurous vapours in volcanic regions on calcareous rocks. When gypsum occurs without water it is called anhydrite, but in its most ordinary state it is combined with water. Research Gypsum
Fibrous plaster is high relief decorative plaster work used to form cornices and mouldings, wall panels, ceiling centrepieces and similar works. Fibrous plaster generally consists of plaster of Paris retarded by the addition of glue size, spread thin and strengthened with scrim and wooden lathes. Research Fibrous Plaster
Gesso is a composition of whiting and glue - sometimes plaster of Paris and glue or size - used for the execution of relief work on woodwork and plaster. Gesso can be modelled when wet and carved when dry. Research Gesso
Abbreviations
Research Fracture
