N I S N I T 515 in the wars of the Romans and the Parthians, its brick walls being unusually thick and its citadel very strong. Ceded to the Parthians by Hadrian, it became a Roman cjlony (Septimia Colonia Nisibis) under Septimius Severus. It was heroically defended against Sapor II., who unsuccessfully besieged it thrice. In the peace made by Jovian, however, it passed into the hands of the Persians, who established a strong colony there. Nisibis early became the seat of a Jacobite bishop and of a Nestorian metropolitan, and under the Arabs (when it continued to flourish and became the centre of the district of Diyar Rebi a) the population of the town and neighbour hood was still mostly Christian, and included numerous monasteries. According to Ibn Haukal the taxes and dues derived from the town and district of Nisibin in 358 A. n. (969 A. D.) amounted to five million dirhems and 32,000 dinars. Arab geographers and travellers of the Middle Ages speak in high terms of the gardens of Nisibis, and the magnificent returns obtained by the agriculturist. According to Mukaddasi (ob. 1024), acorns, preserved fruits, and manufactured articles such as carriages, inkstands, &c., were exported. A change for the worse soon afterwards set in. The town was so heavily burdened with taxes by the Hamdanid princes living at Mosul that the Arab tribe of the Banu Habib, although blood relations of the Hamdanids, migrated in a body into Byzantine territory, where they were well received, accepted Christianity, attracted other emigrants from Nisibis, and at last began to avenge themselves by yearly raids upon their old home. Ibn Haukal goes on to say that finally the Hamdanid Nasir ad-Daule took possession of the town, confiscated the estates of those who had emigrated, and compelled those who remained to substitute corn for their profitable fruit crops. This made a final end of the prosperity of Nisibis; the surrounding district, no longer protected against the incursions of nomad tribes, ceased to be cultivated and became the wilderness which it continues to be to this day. NISI PRIUS. For the history and meaning of this term in English law see ASSIZE. As a rule actions only are tried at nisi 2^us, and a judge is said to sit at nisi prim Avhen he sits alone, usually in the Queen s Bench Division, for the trial of actions. The trial at nisi prius was formerly by jury, unless with consent of the parties, but since the rules of the Supreme Court of 1883 the ordinary trial at nisi prius is without a jury in all but some specially excepted cases, chiefly of torts where the damages are unliquidated. Besides actions, indictments or informations may be tried at nisi prius, but only before a jury, the change in the law above-mentioned not extend ing to such cases. The indictment or information is generally removed from the ordinary forum by certiorari, and the trial takes place in the Queen s Bench Division or at assizes before a special or a common jury (see JURY). The removal may be at the instance of the crown, the prosecutor, or the accused. Misdemeanours are removed more often than felonies. The most usual grounds of removal are that difficult questions of law are likely to arise, that local prejudice has been excited, or that the case is quasi-civil, as non-repair of a bridge or obstruction of a highway. It is noticeable that criminal cases tried at nisi prius take their place in the nisi prius list and not with other criminal cases. Where the proceedings are by indictment at assizes, sentence may be passed either at the assizes or in the Queen s Bench Division ; where by infor mation, only the latter course is available. Nisi Prius Record was before the Judicature Acts the name of the formal copy of proceedings showing the history of the case up to the time of trial. After the trial it was endorsed with the postea, show ing the result of the trial, and delivered by the officer of the court to the successful party, whose possession of the postea was his title to judgment. Since the Judicature Acts there is no nisi prius record in civil actions, the nearest approach to it being the deposit of copies of the pleadings for the use of the judge, and there is no postea, the certificate of the associate or master as to the result of the tiial superseding it. In crown practice, the class of practice under which criminal proceedings &t niri prius fall, the nisi prius record still exists, crown practice being specially excepted from the operation of the Judicature Acts. NISSA. See NISH. NITRATES, NITRE, NITRIC ACID. See NITROGEN. NITROGEN is a chemical element which, on account of its abundance in nature and its relations to life, is of great importance. About three-fourths of the mass of the atmosphere consists of elementary nitrogen; and, as an essential component of all alburnenoids, the element per vades the whole of the animal and vegetable kingdom. Nitrogen minerals are scarce (almost the only ones are Chili saltpetre and native nitre), but traces of the two nitrogen compounds, ammonia and nitric acid, are diffused through out all soils, besides existing in the atmosphere. Elementary nitrogen exists only in the one form of nitrogen gas (N 2 = 1 molecule), which is easily extracted from the atmosphere. Though resembling air in its general properties, it is easily distinguished from it by its not supporting combustion. According to Regnault, its specific gravity is O970.3 times that of pure, dry air; and one litre, measured at t C. and P millimetres pressure (strictly speaking the pressure exerted by a column of mercury of C. and the height P, at latitude 45 and sea- level) is W grammes, where For sea-level and lat. 55 54 (Edinburgh or Glasgow) the constant is 45090 ; for lat. 51 32 (London), 0-45072. According to Dittmar (Reports on the Challenger Expe dition) 1000 volumes of pure water, when shaken with excess of gas at t C. and " one atmosphere s pressure," absorb (3 volumes of the gas measured at and the same pressure, ft having for the temperatures given the fol lowing values : t= = 24-40 15 17-65 25 14-95 30 13-90 Nitrogen is a permanent gas in this sense that no amount of pressure will liquefy it at any temperature lying above the "critical point" of - 123 8 C. At or a little below this temperature 42 atmospheres reduce it to a liquid (Sarrau). Chemically, nitrogen gas is characterized by perfect inertness towards all ordinary reagents under ordinary conditions. But at certain higher temperatures boron, magnesium, vanadium, and titanium combine with it directly into nitrides. Nitrogen is capable even of uniting with ordinary oxygen. A mixture of the two gases, it is true, remains unchanged when exposed en masse to any tem perature, but when it is subjected to a succession of electric sparks a small proportion of the two gases, no doubt through local dissociation into isolated atoms N and 0, does unite into nitric oxide, NO, which then combines with more oxygen into red fumes of peroxide, N 2 O 4 . The part which the nitrogen gas in the atmosphere plays in the economy of nature is as yet a mystery. It certainly is not susceptible of being taken up directly by the plants and utilized in their synthesis of nitrogenous compounds. It plays no active part in the processes of combustion and of animal respiration ; in either it appears to act only as an inert diluent of the oxygen. In the case of respiration, however, this particular diluent seems to be essential ; no animal could live healthily for any considerable period of time in pure oxygen, and we know of no other diluent which could be substituted for the nitrogen without producing poisonous effects. Besides, there can be no doubt that atmospheric nitrogen, in an indirect way, contributes towards the building up of nitrogenous organic matter. Every process of ordinary combustion probably, and every electric dis charge in the atmosphere certainly, induces the formation of some nitric acid, which by combining with the atmo spheric ammonia becomes nitrate of ammonia, and from certain experiments of Schonbein s it would appear that nitrogen gas and water are capable of uniting directly into nitrite of ammonia (N 2 + 2H 2 O = N0 2 . NH 4 ), which, sup-
