204 ARROW GRASS 



reddish-brown quartz crystals ; near Iglo in Hungary, 

 it is accompanied with calcareous spar, ochry-brown 

 iron-ore, and copper-green ; near to Schernnitz in 

 Hungary, its accompanying minerals are brown-spar, 

 silver-ore, and g-ak-ra ; at Salfeldt, the principal 

 mineral with which it is grouped is compact brown 

 iron-ore, along with blue copper, and pyramidal cal- 

 careous spar ; and it is found in compact lime-stone 

 at Wolfstein in the Upper Palatinate. It is fre- 

 quently found in Scotland, where it occurs along with 

 galena, and in the secondary trap-rocks. 



A R T A B O T R Y S. 



of garlic which results from raising its temperature. 

 This however is a test that should be employed with 

 care, as the arsenical vapour which produces this 

 odour is in the 1 ighest degree acrid and poisonous. 

 It is electro-negative, and belongs to that class of 

 metals whose oxides rather act as acids than bases, in 

 the compounds they form with other oxidated bodies. 



Native arsenic when fresh fractured is of a whitish 

 grey colour. It occurs massive, and is externally 

 either rough or granulated. 



It is generally found in veins in gneiss, micaceous- 

 slate, and clay -slate ; and is a frequent precursor of 

 rich masses of silver or cobalt : it is also associated 

 with red silver, sulphuretted silver-ore, and arsenical 

 pyrites. The mines of Kongsberg in Norway 

 produce it in considerable quantities ; as also do 

 those of Saxony, Silesia, Suabia, and Hungary. The 

 accompanying sketch is taken from a specimen from 

 Nagyagin, Transylvania. 



Arragonite. 



The coralloidal arragonite, like the preceding 

 species, is massive in its character, but the fragments 

 have a peculiar wedge-shaped appearance. 



ARROW GRASS (Triglochin of botanists.) A 

 family of bog plants, mostly natives of Europe. There 

 are six species : three of which are found in Britain. 



ARROW HEAD. The Sagittaria of botanists : 

 a genus of fourteen species found in low marshy 

 places in all quarters of the world. Linnaean class and 

 order Moiuzcia Polyatidria , natural order, Alismacece. 

 Generic character: flowers perfect monoecious and 

 dioacious ; calyx three sepaled ; corolla three pe- 

 taled ; stamens inserted on the receptacle ; filaments 

 like threads ; anthers ovate, double ; cells discretous, 

 opening outwards ; styles numerous, very short ; stig- 

 ma acute, persisting ; caryopses numerous, bard ; 

 seeds albumenous. This genus receives its name 

 from the shape of the leaves being like the head of 

 an arrow ; often seen in the shallow parts of lakes and 

 rivers. 



ARROW ROOT of the druggists, and MA- 

 RANTA of botanists. A family containing fourteen 

 species, all considered ornamental : natives of the tor- 

 rid zone. Linnaean class and order Monandria, Mono- 

 gynia ; natural order Canncce. Generic character : ca- 

 lyx double, both sides three-parted superior ; corolla 

 one petaled, three-cleft, leaning back, segments 

 thrice two-parted ; stamens, filaments like petals, 

 two-parted, bearing one anther, style twisted ; stig- 

 ma three-sided. Maranta arundinacea yields the 

 nutritive faecula of the shops. 



ARSENIC, a mineral which appears to have been 

 one of the first known in medicine ; it was also used 

 to a considerable extent for the purpose of painting, 

 even in the time of Theophrastus. It presents a 

 variety of appearances dependent on the various 

 bodies with w hich it is combined in its mineral state ; 

 but one very marked peculiarity is the strong odour 



Arsenic. 



We may now enumerate some of the principal 

 mineral combinations of arsenic. Arsenical silver is 

 massive in its character, and has a specific gravity of 

 9.440. It is found in Germany and Spain. 



Arsenical pyrites is usually divided into two 

 species ; prismatic arsenical pyrites and di-prismatic 

 arsenical pyrites. The first of these is of a pale 

 steel grey colour, with a metallic and shining lustre : 

 it occurs massive, in the form of oblique four-sided 

 prisms. This species is again sub-divided into 

 common arsenical pyrites, and argentiferous arsenical 

 pyrites ; the latter occurs abundantly in Cornwall 

 and Devonshire, as well as in the north of Europe. 

 It is from this one that the white oxide of arsenic is 

 principally obtained, and artificial orpiment is also 

 prepared from it. 



Argentiferous arsenical pyrites is distinguished 

 from the last named mineral by its inferior lustre and 

 the smallness of its crystals ; it is of rare occurrence, 

 and is almost exclusively confined to the north of 

 Europe. 



Arsenic oxide nearly resembles PHARMACOLITH , 

 which see. 



ARTABOTRYS (R. Brown). A sweet scented 

 ornamental evergreen shrub, introduced from China. 

 Linnaean class and order Polyandria Polygynia ; 

 natural order Anonacece. Generic character : calyx 

 three parted, larger than the corolla ; segments lan- 

 ceolate ; corolla six-petaled, alternately roundish and 

 pointed ; stamens below the germen ; style very short, 

 and simple ; berries attenuated on each side, two- 

 seeded. 



