PRU 



PSI 



where it was discovered. This substance 

 is now formed, chiefly, during the decom- 

 position of animal substances in high tem- 

 peratures. Three parts of blood, evapo- 

 rated to dryness in an iron dish, are to be 

 mixed with one part of subcarbonate of 

 potash, (common pearlash) and calcined 

 in a crucible, which should be only two- 

 thirds filled by the materials, and covered 

 with a lid. The calcination must be con- 

 tinued, with a moderate heat, as long as 

 a blue flame issues from the crucible ; 

 and when it becomes faint, and likely to 

 be extinguished, the process must be 

 stopped. Throw the mass, when cold, 

 into ten or twelve parts of water ; allow 

 it to soak a few hours, and then boil them 

 together in an iron kettle. Filter the li- 

 quor, and continue pouring hot water on 

 the mass as long as it acquires any taste. 

 To this solution, add one composed of 

 two-parts of alum and one of sulphate of 

 iron, in eight or ten of boiling water, and 

 continue the mixture as long as any effer- 

 vescence and precipitation ensues. Wash 

 the precipitate several times with boiling 

 water. It will have a green colour ; but, 

 On the addition of a quantity of muriatic 

 ac;d, equal to twice that of the sulphate of 

 iron which has been used, it will assume 

 a beautiful blue colour. Wash it again 

 with water, and dry it in a gentle heat. 

 In this state it is the pigment, called Prus- 

 sian blue, which consists of a mixture of 

 prussiate of iron with alumine. From 

 prussiate of iron, the prussic acid may be 

 separated by the following process : mix 

 two ounces of red oxide of mercury, pre- 

 pared by nitric acid, with four ounces of 

 finely powdered Prussian blue, and boil 

 the mixture with twelve ounces of water 

 in a glass vessel, shaking frequently. 

 Filter the solution, which is a prussiate 

 of mercury, while hot, and when cool, add 

 to it, in a bottle, two ounces of iron fil- 

 ings, and six or seven drachms of sulphu- 

 ric acid; shake these together, decant 

 the clear liquor into a retort, and distil off 

 one-fourth of the liquor. The distilled 

 liquor is the prussic acid, which combines 

 with alkalies and earths, and has many of 

 the properties belonging to the other 

 acids. It has a sweetish taste, and a smell 

 resembling that of bitter almonds; it 

 does not redden blue vegetable colours. 

 It precipitates sulphurets, and curdles 

 soap. It separates alumine from nitric 

 acid. Oxygenized muriatic acid entirely 

 decomposes it. It does not appear to have 

 a strong affinity for alkalies, nor does it 

 take them from carbonic acid, for no ef- 

 fervescence arises on adding it to a solu- 



tion of alkaline carbonates; on the con- 

 trary, its combinations with alkalies and 

 earths are decomposed by exposure to 

 carbonic acid, even when highly dilut-d, 

 as in atmospheric air. It readily com- 

 bines, however, with pure alkalies, de- 

 stroys their alkaline properties, and forms 

 crystallizable salts. It does not precipi- 

 tate iron blue, but green, and this green 

 precipitate is soluble in acids The rays 

 of light render the green precipitate b;ue, 

 as does also the addition of metallic iron, 

 or sulphurous acid. 



PSIDIUM, in botany, guava, a genus 

 of the Icosandria Monogynia class and 

 order. Natural order of Hesperidx. Myr- 

 ti, Jussieu. Essential character: calyx 

 five-cleft superior ; petals five ; berry 

 one-celled, many seeded. There are 

 eight species, natives of the East and 

 West Indies. 



PSITTACUS, the parrot, in natural his- 

 tory, a genus of birds of the order Picx. 

 Generic character: bill hooked, upper 

 mandible moveable ; nostrils round in the 

 base of the bill, and sometimes covered 

 with a cere; tongue fleshy, broad, and 

 blunt at the end ; head large, crown flat : 

 toes formed for climbing. These abound 

 within the tropics, and live on seeds and 

 fruits in their natural state, but in confine- 

 ment will eat both flesh and fish. They of- 

 ten appear in flocks, yet are in such cases 

 general ly somewhat separated into pairs. 

 They are noisy, mimetic, singularly ca- 

 pable of articulating human sounds, ex- 

 tremely docile, and Jong lived They 

 breed in the hollows of trees, without con- 

 structing any nest, and use their feet as 

 hands to convey food to their mouths. 

 Latham notices one hundred and thirty- 

 three species, and Gmelin no fewer than 

 one hundred and sixty nine. The gene- 

 ral division is regulated by the evenness 

 or unevenness of the tails. The follow- 

 ing are the principal species. 



P. macao, or the red and blue maccaw, 

 is as large as a capon, and inhabits South 

 America- With its bill it breaks a peach- 

 stone with the most perfect ease. These 

 birds lay their eggs in decayed trees, and 

 often enlarge the hollow for this purpose 

 with their bills. They are used tor food 

 in vast numbers in Cayenne. They are, 

 in common with many species, exposed to 

 fits when confined. 



P. rufirostris, or the long-tailed green 

 parrakeet, is of the size of a blackbird, 

 extremely clamorous, and highly imita- 

 tive. These birds are seen in large flocks, 

 and alighting on certain trees, can with 

 difficulty be distinguished, in consequence 



