465 



PHOSPHORUS, MEDICAL PROPERTIES OF. 



PHOTOGRAPHY. 



468 



combustion of phosphorus in chlorine gas; a white, flaky, volatile 

 compound is formed, which is the perchloride. It is volatile, rising in 

 vapour at 2uO. It is fusible under pressure, and crystallises in priams. 

 It reddens dry litmus-paper, owing, as has been suspected, to its 

 acquiring oxygen and hydrogen from the decomposition of the paper. 

 Like the protochloride, it acts strongly upon and decomposes water ; 

 but the results are hydrochloric acid and phosphoric, instead of 

 phosphorous, acid. 



Pkusphide of Nitrogen (PN a .'). This compound cannot be obtained 

 by direct action ; it is the result of the action of ammonia on the 

 chlorides of phosphorus. The changes which occur are effected with 

 difficulty, but the phosphide of nitrogen eventually obtained has the 

 following properties : It is a light white powder, and, although 

 formed of very volatile constituents, it remains fixed and infusible 

 even at a red heat, when the access of air is prevented ; but if that be 

 present, white vapours of phosphoric acid are formed. This compound 

 is remarkable, also, for its indifference even to the most powerful 

 re-agents ; it is insoluble in water and in acids, nitric acid even attack- 

 ing it only after long continued exposure to it. Chlorine and sulphur 

 do not act upon it; it is insoluble in alkaline solutions, but when 

 heated with solid hydrate of potash, ammonia is evolved. According 

 to Gerhardt, it contains hydrogen, and its formula is HN,P. 



Sulphur and Phosphorus may be made to combine in all proportions 

 by fusion in an exhausted flask or under water ; but the operation 

 requires great caution. The resulting sulphides are very inflammable, 

 and mostly crystalline. 



Phosphorus and Iodine. [IODISE.] 



Phosphorus and Uromine. [BBOMINE ] 



Phosphorus may be made to combine with the greater number of 

 the metals ; the most important of these compounds (phosphides) will 

 be found under each particular metal. 



Detection of Phosphorus. Phosphorus is very poisonous. It is 

 readily detected in a mixture containing organic matter by placing the 

 suspected mixture in a flask, adding sulphuric acid, suspending a piece 

 of paper streaked with solution of nitrate of silver from the upper part 

 of the flask, and gently heating ; if phosphorus be present, the paper 

 will exhibit black marks of phosphide of silver. The absence of sul- 

 phuretted hydrogen, and of arsenic, must be previously ascertained ; 

 the one by acetate of lead paper suspended in the flask, the other by 

 Marsh's test. 



Detection and Estimation of Phosphoric Acid. One of the best tests 

 for phosphoric acid is the production of a white crystalline precipitate 

 in the presence of ammonia, on the addition of a soluble salt of mag- 

 nesia. The resulting ammonio- phosphate of magnesia, on being ignited, 

 is converted into phosphate of magnesia, which contains 63'33 per cent, 

 of phosphoric acid. 



PHOSPHORUS, MEDICAL PROPERTIES OF. This elementary 

 substance exists as an essential constituent both of vegetable and 

 animal bodies ; yet when applied in a concentrated and pure state to 

 any organised structure, it acts upon it as a violent and corrosive 

 poison. Into animal bodies it is introduced in a diluted and combined 

 state, by which it is disarmed of its virulence, as an ingredient of 

 many common articles of food. One of the chief sources of it is the 

 starch of the cereal grains, such as wheat-flour, in the ashes of which, 

 when burnt, it amounts to 23 per cent. (Prout's ' Bridgewater Treatise,' 

 book iii.) ; also alliaceous plants, such as onions, in which it exists as 

 a phosphate of iron ; polygonous and other plants, in which it occurs 

 as a phosphate of lime. It also exists not only in the bones and other 

 hard parts of animals, but in many of the fluids, especially the excre- 

 tions. Thus it is found in the milts and roes of fishes, the substance of 

 oysters, the yelk of eggs, in the liver, and also the brain, in which 

 organ of the human being it amounts to from 2 to 24 per cent. 



Phosphorus is of all stimulants the most powerful and diffusible, 

 but, on account of its activity, highly dangerous. Its poisonous action 

 seems to be connected with its strong affinity for oxygen, by which it 

 is converted into phosphorous and phosphoric acids. Hence when 

 brought into contact with the animal tissues, it abstracts oxygen from 

 them, and produces an eschar, resembling a burn : the phosphorus in 

 this way loses weight and is absorbed, so that the exhalation from the 

 lungs and the cutaneous perspiration are impregnated with the vapour, 

 and, under certain circumstances, luminous. A very small quantity of 

 solid phosphorus, even one grain and a half, has proved fatal. Solu- 

 tions of phosphorus in oils, fixed or volatile, or in ethers, are still more 

 active and dangerous. The vapour of phosphorus is accused of causing 

 a peculiar affection of the jaw-bone in persons working much with it, 

 such as manufacturers of congreve matches. This evil may be pre- 

 vented by wearing a sponge before the mouth and nostrils, and the 

 observance of great cleanliness, especially using a solution of soda for 

 washing the hands. Acetate of potash is useful in the dysuria which 

 follows poisoning by phosphorus. 



Little use is made of phosphorus or its oleaginous solutions in 

 medical practice in Great Britain, though in cases of extreme prostra- 

 tion of the nervous system it is not without its value. 



In the event of a poisonous dose being taken, bland mucilaginous, 

 not oily, fluids should be freely administered, followed by magnesia or 

 chalk in boiled water. 



PHOSPHURETTED HYDROGEN. [PHOSPHORUS.] 

 PHOTOGRAPHY is both an art and a science. As an art it enables 



AXT* AND 801. DIV. VOL. VI. 



us to draw, depict, or write by means of light. As a science it teaches 

 us how to observe and to investigate the effects produced by light 

 upon all natural bodies, whether animate or inanimate, mineral, vege- 

 table, or animal. Its study as an art is of comparatively recent date, 

 but the science had previously excited the attention of nearly all the 

 most eminent investigators in modern science. The names of Davy, 

 Wedgwood, Thomas Young, Wollaston, and the two Herschels in this' 

 country of Scheele, Ritter, Seebeck, Berthollet, and Becquerel on the 

 Continent testify to this effect. Photography is worthy of special 

 attention from the fact that it requires for its rational and thoroughly 

 successful pursuit a knowledge of chemistry, optics, and physics gene- 

 rally, together with an amount of artistic taste and manual dexterity, 

 such as must be useful not only for purposes of mental training, but 

 under a variety of circumstances in actual life. The variety of its 

 parts and aims gives it a special charm for those who like to have a 

 pursuit admitting of both activity of mind and body ; its processes are 

 as much carried on out of doors as in close laboratories. Further it 

 has this charm, that while it furnishes problems of the greatest 

 interest and intricacy for the most advanced philosopher in optics or 

 chemistry, it has its practical processes, which may be readily appre- 

 hended, and exercised for purposes of utility or recreation by those who 

 are but little skilled in physical manipulations. 



The history of photography has been so fully treated of by Mr. 

 Robert Hunt, in his ' Researches on Light,' and in his ' Treatise on 

 Photography,' and also by the Abbe 1 Moiguo, in his ' Repertoire d'Op- 

 tique Moderne,' that we need not do here more than recapitulate in a 

 brief manner the points of chief interest which they have given at 

 greater length. 



It may be well to say at the outset, that it was not till the year 1839 

 that Photography acquired for itself distinct recognition, through the 

 investigations of Fox Talbot and Daguerre, which resulted in the 

 introduction of the two processes known as the Calotype or Talbotype, 

 and Daguerreotype. As usual in the history of art and science, 

 approximations had been attained to by earlier experimentalists. It is 

 interesting to inquire into the labours of some of these. Proceeding 

 historically, we shall find that observations relating to the science of 

 photography precede the first attempts at establishing the principles of 

 the art. 



In 1722 Petit noticed that solutions of nitrate of potash and 

 muriate of ammonia crystallised more readily in the light than they 

 did in darkness. In 1777 Scheele wrote, "It is well known that 

 the solution of silver in acid of nitre, poured on a piece of chalk 

 and exposed to the beams of the sun, grows black. The light of the 

 sun reflected from a white wall has the same effect, but more slowly, 

 heat without light being without effect." Again, " Fix a glass 

 prism at the window, and let the refracted sunbeams fall on the 

 floor. In this coloured light put a paper strewed with tuna cornua 

 (chloride of silver), and you will observe that this horn silver grows 

 sooner black in the violet ray than in any of the other rays." 



Senebier repeated these experiments, and also experimented on the 

 influence of light in the bleaching of wax. 



In 1798 Count Ruinford sent to the ' Philosophical Transactions' 

 a memoir entitled ' An Inquiry concerning the Chemical Properties 

 that have been attributed to Light.' In this paper the Count attempts 

 to prove that all the effects produced upon metallic solutions by bright 

 sunshine are due to heat. In 1802 Mr. Harrup refuted this view, and 

 showed that several salts of mercury were reduced by light alone, and 

 not by heat. 



In 1801 Ritter proved the existence of rays in the solar spectrum, 

 which are to be found beyond its visible limits, and that these rays have 

 the power of darkening chloride of silver. These researches having 

 excited attention, MM. Berard, Seebeck, Berthollet, Sir W. Herschel, Sir 

 H. Englefield, Wollaston, Davy, and others, made various experiments 

 which tended still further to confirm the proof that light had a special 

 influence over bodies beyond that exercised through its heat ; and 

 that the colour of the light was in some way related to this newly 

 observed action of the sunbeam. 



Before proceeding to notice the early efforts of those who laid the 

 foundation of the art of photography, with which we are now to be 

 chiefly engaged, we may observe that Priestley, Senebier, Ingenhousz, 

 De Candolle, Saussure, and Ritter, directed attention to the influence 

 of light upon plants an interesting and important subject. Others 

 followed in a similar track, still, however, leaving the matter in a com- 

 paratively obscure condition. The action of light on the human frame, 

 and on animal life generally, has not yet been fairly investigated. 

 That some special action will be detected there can be no doubt. We 

 have long thought that light will come to be considered as impor- 

 tant an element to health as fresh air and wholesome food. It may 

 possibly be that much mental or bodily labour, exercised in the 

 absence of the stimulus of daylight, is indirectly injurious to 

 animal life. 



But let us proceed to trace rapidly the art of photography to its 

 source. In the Journals of the Royal Institution of Great Britain 

 for 1802 will be found a paper by " Thomas Wedgwood and Hum- 

 phry Davy" the first a brother of the famous porcelain manufacturer, 

 the second the Sir Humphry Davy of a later period. Their joint 

 paper was entitled ' An Account of a Method of Copying Paintings 

 upon Glass and of making Profiles by the Agency of Light upon 



H B 



