A few years ago, Prof. Graham, Director of the Royal Mint in London, discovered that a certain class of substances could be more readily diffused through water than others; he found, for example, that salt, sugar, gum, % and dried albumen, if placed in different vessels, and covered with water, will all of them be diffused through the water, but not in the same period of time. The salt spreads rapidly; the sugar requires twice the time, the gum four times, and the albumen twenty times longer. He found, as a rule, that substances which crystallize are diffused more rapidly than those which are amorphous. The first class are called crystalloid, and the second class colloid. When they are both in solution we can employ a thin membrane, or a piece of parchment paper, and, as it were, filter or strain the crystalloid through its pores, while the colloid remains behind. This operation is called dialysis, and the contrivance for effecting it, is known as the dialyser. A sieve, a half barrel, a drum, a glass jar open at both ends, or even porous earthen cells, will serve for the apparatus. By tying a piece of bladder, or of parchment paper, over one end of any of the above pieces of apparatus, and floating it upon water, we have all that is required. If we pour into such a contrivance a solution of albumen and of common salt, and partially sink it into a larger vessel filled with fresh water, the common salt will very rapidly strain through the membrane into the outer water, and leave all of the albumen behind. Even silicic acid, which crystallizes in the form of quartz, can be separated from compounds in this way, provided it has been previously fused with soda. Graham has performed a series of experiments upon a large class of bodies, a ecapitulation of which may suggest some practical applica-;ions of his simple device. He discovered that tannic acid diffused through parchment mper two hundred times more slowly than common salt, and inds in this fact an explanation of the reason why it takes ;annin so long to penetrate hides so as to convert them into eather. All processes for making leather rapidly will be ?ound to be based upon the facility with which the substances employed pass through membranes, and the agents used are generally composed of crystalline salts. We are not aware of my practical application of Prof. Graham's discovery to the banning of leather, but it is certainly worthy of the attention of persons engaged in the business. Gum-arabic diffuses four hundred times more slowly than salt, and hence belongs to the class called colloid. The method of dialysis can be employed for the detection of irsenic, emetic, corrosive sublimate, or any crystalline poison, in the stomach, blood, milk, or any organic 'compounds. The poisons will pass through the membrane inj;o the outer vessel, and their presence can be shown bythe" usual tests. The same process can be made available in the case of organic poisons, such as strychnine and morphine, and it is further valuable as a method of original research in seeking for alkaloids in any new plants, and it has even been proposed as the best way for the preparation of alkaloids on a large scale. Many plants contains niter and other mineral salts, which can be separated and detected by dialysis better than in any other way. Nitrate of silver, from photographers' waste, when put into the dialyser, passes through to an outer vessel, where it can be precipitated and saved ; the albumen and other organic matter will remain in the inner vessel. For this purpose a half barrel, with parchment tied over the bottom, and immersed in a barrel of water, would be a good contrivance. Great expectations were raised in reference to the separation of sugar from molasses, and its purification by dialysis. Several patents have been taken out for this purpose. At the Paris Exhibition of 1867, Messrs. Carmichel Co., sugar refiners and distillers, exhibited dialysers for refining sugar, which they called osmogenes. Each apparatus contained fifty or sixty frames, forming partitions one-quarter of an inch in thickness, and furnished with nettings of strings to support the sheets of parchment paper destined to accomplish the work. The frames with water alternate with those for molasses or sirups. Each frame is provided with an interior opening for the hot water, and another for the sirup, so arranged that each section receives, the one the water, the other the sirup. Both liquids start from a hight of three feet, and, after descending to the bottom of the apparatus, return again, at a temperature of 160 to 170 Fahrenheit, and pass out at the top. The water is introduced and regulated according to the extent of purification required. The inventors of this apparatus claimed for it very important results, and as it was founded upon thoroughly scientific principles, we see no reason to doubt the truth of their statements. The process is particularly valuable in the manufacture of beet sugar, and for removing potash and lime salts from sirups, but it does not appear to have been generally adopted, probably because it is not well understood. Mr. Whitelawtook out a patent in England, in 1864, for the removal of salt and niter from salted and corned meats by means of dialysis. It is well known that the brine contains a large proportion of the nutritious constituents of the meat, and if we could remove the salt and evaporate the residue we should have all of the properties of a good soup. It so happens that the savory and valuable constituents of meat are colloids, and will not, therefore, pass through a membrane. The salt, which is added to keep the meat from decay, is crystalline, and, as we have before seen, passes very readily through parchment. Mr. Whitelaw takes advantage of these two facts, and puts the brine into porous jars or bladders, which he suspends in water, that must be renewed three or four times in twenty-four hours. After a few days, the contents of the jars will be found to be fresh and sweet, ready for use as soup, or they can be evaporated down to dryness and converted into meat biscuit. In this country, where such large quantities of corned and salted meats are consumed, the saving of the brine is a matter of much practical importance, particularly as what is thrown away is too often the most nourishing portion of the food. FILTERING OXYGEN FROM THE AIR. The same principle of dialysis was successfully applied by Graham to the concentration of the oxygen in the air. By passing air through shavings of india-rubber, the rubber retains a portion of the nitrogen, and the quantity of oxygen is increased to forty-one per cent., being twenty per cent more than its usual capacity. An atmosphere with forty-one per cent of oxygen will re-ignite a glowing taper, and, in general, support combustion and respiration in a very active manner. The experiment points out such a simple and cheap way of procuring oxygen from the atmosphere, that it ought to be put to a thorough trial before more money is expended in complicated and costly methods. If, by filtering the air through a membrane, or shavings, or any cheap substances, we can get rid of the nitrogen, we have made a discovery of the highest importance, and the experiments of Graham certainly seem to point out the feasibility of the plan. Certain physiological phenomena can be very well explained by the doctrine of dialysis ; for example, according to Professor Daubeney, of Osford, gums, starch, oil, or any similar class of bodies secreted in the cells of plants, must be classed among the colloids: they have no tendency to pass through the walls of the cells where they have been elaborated, and consequently arrange themselves into groups. On the other hand, the acids and alkalies are crystalloids, and pass freely through the pores of the cslls, and are frequently found on the outside, or they pass to the organs of the plant, where they undergo transformation by action of the vital force. The mucous membrance of the stomach may be compared to the parchment of the dialyser the crystalloid elements are absorbed, while the colloid remain to be subjected to the action of the gastric juice, which elaborates them according to the laws of nutrition. The action of different kinds of medicines can be explained according to the same law. Those which are crystalloids will diffuse rapidly through the coating of the stomach, while the amorphous medicines will remain, subject to the action of the gastric juice and the laws of digestion. The application of dialysis in the dry way has been proposed by a French savant. He assumed that substances which fused at different temperatures could be separated by passing-them through a porous vessel on the same principle. Such an application would be most valuable in metallurgy, but thus far it has not been reduced to practice. In the manufacture of paper from sea-weed, after the weeds h ave been boiled in caustic soda, the black liquor is thrown away. It would be well to put the waste liquor into porous cells, suspended in tanks of fresh water, to see if the crystallizable salts of iodine would not pass into the outer vessel, where they could be reclaimed. We have thus hastily noticed some of the leading a pplica-tions of dialysis. It is a process so very easy, so simple, and so cheap, that it only needs to be better understood to acquire great popularity. Journal of Applied Chemistry. Alleged discovery of Petroleum at Wismar. A strange rumor, says the Grocer, is afloat in Germany of the discovery of a petroleum spring at the seaport town of Wismar, in the Grand-Duchy of Mecklenburg-Schwerin. Our Hamburg correspondent informs us that, on March 19th, the workmen employed in digging out the earth for the new sewers in course of construction on the promenade surrounding-the town, came suddenly, at a depth of five feet below the surface, upon a spring of oil, which proved to be petroleum of excellent quality, pure, and limpid. It was at first surmised that it might be caused from the leakings from the gas works at no great distance off, but the officials of that establishment declared that such was not the case. The news spread through, the town like wildfire, and, in a very short time, hundreds of people rushed to the spot with bottles and pitchers, which they filled with the liquid, and Herr Beckmann, the chemist of the corporation, carried away a sample for the purpose of analyzing it. When one considers that the geological formation of that part of Germany is purely alluvial soil, or at the very oldest of diluvial origin, while the total absence of all rocks, and, on the other hand, the abundance of erratic blocks of Swedish granite of all colors and sizes, covering the surface, suggests a reference to the glacial period, it certainly does appear extraordinary that an oil spring should have been struck within five feet pf the surface of the ground. As far as we have been able to ascertain, there are no artesian or other deep wells at Wismar or in the neighborhood, and, therefore, in the absence of any such borings, it is impossible to ascertain, or even approximately to hazard an opinion, as to the nature of the rocky substratum underlying the diluvial surface, though in some parts of Mecklenburg large beds of marl and gypsum have been discovered at a great depth. --------------,+** --------------. Calculating; Areas l y Weight. The Engineer contains a very novel method for computing areas by weight; an accurate square of homogeneous paper of uniform thickness being used for plotting the map of the area to be measured. The whole is accurately weighed in a delicate balance, and then the tracing of the boundary is cut out, when the weight of the piece cut out, divided by the entire weight of the square will give the ratio of the surface to be measured to that of the square, both being drawn to -the same scale. Areas of the most irregular form may thus be very readily and quite accurately determined. ,, - o ------- -------- The Brazil (Ind.) Miner says that the f urnaco of the Indian apolis Furnace and Mining Company, at Brazil, is the largest establishment of the kind in the United States. The furnace, or rather the double furnace of the Western Iron Company, at Knightsville, two miles east of Brazil, though not so large* as the one first mentioned, has been a paying institution from the start. The cost of the first stock was nearly $100,000, and the profits of the concern paid for it inside of six months after it first commenced operations. Over ninety per cent of the rays issuing from most kinds of artificial lights are according to the German chemist, Landsberg, calorific or heat rays, and as such non-luminous. Sunlight has only fifty per cent of heat rays. He attributes the painful effect of artificial light upon the eyes to this large amount pf heat rays. By passing artificial light through alum or mica, the heat rays are interrupted and the light is rendered much more pleasant and less injurious. A Curious experiment i s said t o hav 3 been recently performed in France to ascertain whether fishes can live in great depths of water. The fish were placed in vessels of water made to sustain 400 atmospheres, under which they lived and preserved their health. It is therefore concluded that fishes? may penetrate to very great depths in the ocean with impunity. During the past seven months, there have been in the United States sixty-one boiler explosions, the great majority of them involving less of life. Improved Brake for Velocipedes. Messrs. Mercer Monod, of No. 3 William street, New York city, are among the most enterprising velocipede men in the city. At their school they use machines of elegant pattern and excellent action, and adopt improvements as fast as suggested. In the accompanying engravings a new improvement is represented for the management of the brake, and for which a patent is now pending through the Scientific American Patent Agency. Fig. 1 is a perspective view of the velocipede with the improved brake. Fig. 2 is an enlarged view of the brake and its contiguous parts. The brake shoe, A, is faced with hard sole leather, or some similar substance calculated to hug the tire closely. It is pivoted in a slot through the reach and furnished with a spring, B, that lifts it from the wheel when not forced against the wheel's perimeter by the rider. Its upper end is connected by a forked rod, C, to an arm of a bell crank lever, pivoted just in rear of the driving wheel support to the clip, which also sustains the saddle spring. The other arm of the bell crank is engaged with a strap that may be wound up on the steering bar, D, that revolves in its standards. It is evident that by this device the ride* has entire and perfect control of his vehicle by his hands, the whole muscular force of the arms being readily applied at will. In no case, however, is this force required, only a slight sxertion being necessary to prevent the wheel from revolving, even going very steep grades. The adaptation of this brake in no wise weakens the vehicle in any of its parts, and it presents an elegant appearance. Further information may be had of Mercer Monod, No. 3 William street, New York city. ----------------------------- : Hlmmcr's Patent Gasfitters' Tool. The implement shown in the accompanying engraving is designed for fitters of gas, steam, and water pipes of iron, to reduce the number of tools ordinarily carried about, and to provide a handy combination instrument in their stead. By it the pipe is cut, the scale or rust cleaned off, the thread cut to receive the thimble, tee, or cock, and the pipe held while being screwed up. The stock, or frame, holds a rotary cutter, A, with its stud, B, a scraper die, C, and a set of screw-cutting dies, D. The whole are operated by the screw handle, E. The handle, F, is screwed into the opposite end of the stock, to be used only when threading the pipe. It is readily removed by means of a driver fitting a hole in the handle, as in E. For quick removal of the dies the plate, G, is pivoted near one end and slotted near the other. The stud, B, has a cross piece that steadies it, as seen. It is evident that the dies may be replaced by others instantly. When used as a cramp, or wrench, the cutter, A, is removed by pushing out i the pin that forms its axle, when the apex of the stud may 1 be set against the pipe by the screw handle, E, and it is held i firmly between the stud and the jaw, H. i In operation, when it is desired to cut off a pipe, the handle, F, is removed and the pipe inserted under the jaw for cutting ; off, the stud, B, and rotary cutter, A, are forced up by the screw handle, E, the frame, or stock, is rotated, and the work i is readily done. To clean the end of the pipe from corrosion : or scale, the pipe is inserted between the scraper die, C, and its bearing block. The thread is cut by the dies, as in an ordinary screw plate, and the implement is used as a wrench, as ] before shown. Patented Sept. 29,1868, by Jacob Himmel, who may be addressed to the care of Edward Gamm, 126 Hester street, New York city. The patentee wishes to dispose of the entire patent.