AMBLYODON. 



[ 28 ] 



AMMONIA. 



AMBLYODON, Pal. de Beauv.— A genus 

 of Funariaceae (Acrocarpous Mosses), to 

 which is referred a Bryum and Meesia of 

 other authors. 



A. dealbatus, P. de Be&ny. ^Bryum deal- 

 batum, Dicks. 



AMBLYOPHIS, Ehr.— A genus of Infu- 

 soria, of the family Astasisea. 



Char. Unattached; a single (red) eye- 

 speck; a simple flagelliform filament, no 

 tail. One species. 



A. viridis (PL 23. fig. 55). Green; length 

 1-210 to 1-240". 



The anterior end of the body is colourless, 

 and cleft so as to represent a two-lipped 

 mouth. Near the middle of the body is a 

 kind of nucleus (?). 



Dujardin regards this animal SiS&Euglena. 



BiBL.Ehr.Jw/M5.,p.l03;Duj.J??/M5.,p.636. 



AMIBA, Duj. See Amceba. 



AMMONIA, HYDROCHLORATE OR MU- 

 RIATE OF. — This salt crystallizes in cubes, 

 octohedra and trapezohedi"a. When crystal- 

 lized rapidly it forms curious feathery con- 

 gregations (PI. 7- fig. 9). The ciystals do 

 not polarize light. 



AMMONIA, OXALATE OF.— This salt is 

 readily prepared by neutralizing a solution of 

 oxalic acid with ammonia or its carbonate, 

 and evaporating. 



It cr}^stallizes in long slender needles, 

 belonging to the right rhombic j^rismatic 

 system. When mounted in Canada balsam, 

 these form a very beautiful object for the 

 polariscope (PI. 19. fig. 7). 



AMMONIA, oxALURATE OF ; formerly 

 kno\vn as the lithoxanthate of ammonia. 



This salt may be prepared by mixing 

 1 part of mic acid with 32 parts of water and 

 heating the mixtm'e in a porcelain cajjsule 

 until it acquires a boiling temperature. Strong 

 nitric acid, previously diluted with 2 parts 

 of water, is next added in small quantities at 

 a time, until nearly the whole of the uric 

 acid is dissolved. The liquid is then boiled, 

 filtered, mixed with excess of solution of 

 ammonia, and concentrated by evaporation. 

 As it cools, the salt is de})osited in needles 

 or warty groups of crystals. These are freed 

 from the mother-liquor by pressure between 

 blotting-paper, dissolved in warm water and 

 a little solution of ammonia added. On 

 evaporation the pure salt separates. 



The oxalm-ate of ammonia forms one of 

 the most beautiful and interesting substances 

 that can be examined by the polarizing 

 microscope. When a small quantity of its 

 aqueous solution is slowly evaporated on a 



slide, some of it usually ciystallizes in circular 

 disks or veiy flat spheres, consisting of 

 minute needles radiating from a centre and 

 in an intimate state of mechanical adhesion ; 

 sometimes the extremities of the needles are 

 seen projecting beyond the cu'cumference of 

 the disks. The latter appear colourless or 

 yellowish by reflected light; pale or dark 

 brown, or even black by transmitted light, 

 according to their size and thickness. When 

 immersed in Canada balsam, they become 

 transparent, often nothing more being di- 

 stinguishable than radiating lines, indicating 

 the needles of which they are composed. 

 But if examined by polarized light and with 

 the analyser, when these are so arranged 

 that the plane of polarization of the analyser 

 is at right angles to that of the polarizer (the 

 field being black), the disks present the 

 appearance of beautiful little stars, sometimes 

 almost white, at others splendidly coloured, 

 each being also traversed by a black rectan- 

 gular cross (PI. 19. fig. 11). 



On rotating the slide, no change is pro- 

 duced. But on rotating the analyser or 

 polarizer 90°, the arms of the cross appear 

 to rotate, which, as there are no fixed points 

 visible in the disks, gives rise to the appear- 

 ance of the disks themselves rotating. When 

 the analyser has been rotated a quarter of a 

 revolution, the former position of the black 

 cross is occupied by a white one, and the 

 colours of the intermediate parts become 

 complementary to (forming white light with) 

 those which they at first possessed; these 

 appearances being alternately reproduced at 

 each quarter revolution. 



If a plate of selenite is placed beneath 

 the slide, the beauty of the objects is much 

 augmented (PI. 19. fig. 12). On some parts 

 of the slide dendritic aggregations of the 

 needles are seen (PL 19. fig. 11 a). 



Sometimes the colours are disposed in 

 concentric rings; when these are well-defined, 

 a concentric arrangement of the groups of 

 needles is distinguishable on examining the 

 disks by common light. 



A simple experiment will show the origin 

 of the cross and the colours. If eight crystals 

 of any doubly refracting salt be arranged 

 upon a slide in the directions of equidistant 

 radii of a circle, they may be regarded as 

 forming two crosses, alternating in position. 

 If the slide be placed under the microscope, 

 with the plane of polarization of the polarizer 

 and analyser at right angles, and the ciystals 

 be simultaneously rotated andkept in the same 

 relative position, a point will be reached at 



