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Free ammonia in water always indicates organic matter in the process of decomposition. In polluted surface waters it is rarely high, being removed almost as fast as formed by vegetable and animal organisms in the water, and an amount of nitrogen as free ammonia above 0.05 milligramme per liter is unusual, and if it does occur the water cannot be considered as an unpolluted water unless that fact is clearly established by other data. According to the recent experiments which have been made by Prof. Niccolo Vaccaro, connected with the physical department of the University of Genoa, relating to the spectrum of nitrogen in a magnetic field, he finds that when applying the field so that the lines of force run transversely through the tube containing the rarefied nitrogen, in which the electrodes for the discharge are placed at each end of the tube, the phenomena vary to a considerable degree according to the pressure in the tube, the latter being connected to an air-pump. The present researches, which were made with considerable detail, show in general that when using pressures which are relatively high, the spectrum in the tube of rarefied gas increases both ill luminous eect and in the number of lines under the influence of the magnetic field. But for very low pressures the eect is seen to be clearly inverted, and the magnetic field has a weakening eect. He finds that there is a critical point at which no eect is oerved from the field, and this is at a pressure of 0.02 inch of mercury in the tube. At this point the magnetic field has no appreciable influence upon the spectrum of the rarefied gas. A French chemist, L. Ouvrard, has formed a series of new compounds, the boro-stannates of the alkaline earths. He has also succeeded in reproducing the mineral nordenskioldine by artificial means. Researches upon the metallic borates led him to form the boro-stan nates by dierent methods, and among these is the boro-stannate of calcium, which is identical with the above-mentioned mineral. First, he tried by fusion, in chloride of calcium, of a mixture of boric acid or borate of lime and broxide of tin. Here the reaction is not decisive, and no doubt there results a chloro-borate. A better method is to mix in a platinum trough, the precipitated borate of lime, corresponding nearly to CaO, 2B,O3, with a small quantity of broxide of tin coming from the calcination of meta-stannic acid. The trough is placed in a porcelain tube and brought to a white heat, while passing a slow current of hydrochloric acid vapor. After three-quarters of an hour he finds a melted opaque mass, covered with hexagonal scales, some of which are also deposited upon the trough. These scales, when isolated, are found to be the boro-stannate of calcium BO:i, SnO: . CaO. This body is colorless and transparent, and not easily melted. It scarcely dissolves in hydrochloric acid, even when concentrated. The crystalline scales are fragile, with a glassy lustre, and resemble the natural mineral. Some of the largest ones are 0.05 inch wide and 0.0004 thick. This compound is identical with the mineral nordenskioldine, which was described by BrUgger in 1887. By an analogous process, he was able to form the corresponding compounds of strOntium and barium. These. however, are more diicult to produce. Using as above a current of gaseous hydrochloric acid at a red heat he obtains some scales of boro-stannates mixed with numerous crystals of casserite. By reacting upon stannic chloride the results are generally better, and he was able to form the new compounds of barium and strontium in a nearly pure state. These are crystalline bodies having about the same appearance as the calcium compound.
