Cooley's Cyclopaedia of Practical Receipts Volume Ii Part 134

4. If chloride, reduce to oxide by boiling with strong potash, then reduce by glucose; or boil the chloride with glucose and sodium carbonate.

5. Add silver chloride dissolved in ammonia to a boiling solution of one part glucose and three parts sodium carbonate in 40 per cent. of water, keeping up the boiling all the time.

6. Add to silver chloride sodium hydrate in solution and grape sugar, and expose to sunlight in open dish with occasional stirring. Reduce to dark brown oxide of silver, soluble in nitric acid.

7. Mix with five times weight of sodium carbonate. Fill hessian crucible half full, and sprinkle sodium chloride over the top. Heat slowly in anthracite fire. After half an hour increase heat till crucible is white-hot. When complete fusion has taken place, allow to cool, and break out b.u.t.ton of silver.

8. Fuse with two parts mixed carbonates (sodium and pota.s.sium).

9. Add pure zinc and dilute sulphuric acid, and let stand two days. Wash silver off with water acidulated with sulphuric acid, to remove all zinc; finally fuse to a b.u.t.ton.

10. Mix with half weight dry sodium carbonate and one-fourth weight of clean dry sand, and ignite.

IV. _Gold Waste_, a, _Recovered_.

1. Make just acid with hydrochloric acid, add solution containing 2 oz.

pyrogallic acid, shake, let stand 24 hours; filter. Dissolve in aqua regia, and product after evaporation will be found better for toning than that precipitated by iron.

2. Acidify toning bath, and add sulphate of iron (2 grammes to 1 gramme chloride of gold.)

. _Separated from Silver._

1. Treat b.u.t.ton obtained by fusing waste from hypo-toning and fixing baths with dilute nitric acid. Wash insoluble part with ammonia to remove silver chloride, if present, and dissolve in aqua regia.

2. Digest 20 grammes in flask with 1 fl. dr. hydrochloric acid, 15 m.m. of nitric acid, and 2 dr. of water. After quarter of an hour boil, add 2 oz.

water; filter. Silver chloride with organic matter, &c. left undissolved.

Reduced as III, above.

3. Add excess of pure pota.s.sium hydrate, and then boil in flask with excess of solid oxalic acid.

V. _Paper Waste._

1. Soak paper in strong solution of saltpetre, and burn.

2. Treat with nitric acid, precipitate with sodium chloride or pota.s.sium hydrate, then put with III, above, for reduction.

_Washings from Positive Prints._

Precipitate by sodium chloride, pota.s.sium hydrate, or on copper plates, &c., as above, and reduce, as in III.

VI. _Cyanide Solution._

1. Dilute with water, precipitate by (1) pota.s.sium sulphide, (2) sodium chloride, and reduce as 3.

2. Decant bath into iron kettle, warm, add ferrous sulphate slowly till slight precipitate of oxide. Make alkaline, and add solution of grape sugar till brownish-yellow colour. Allow to settle, syphon off liquid.

Wash sediment on filter, and ignite to recover silver.

NOTE.--Ferrous sulphate forms ferrocyanide, therefore no free alkaline cyanide should be present.

VII. _Developer._

1. _Vide_ II. (3, 4, 5, 6), with hypo bath; (1) and (2) not applicable, for sulphide of iron would be formed.

2. Reduced by its own iron (if ferrous sulphate).

=PHOTOM'ETRY.= The art of determining the relative intensities of different lights. Various methods have been adopted, at different times, for this purpose, among which, however, a few only are sufficiently simple for general application. The principle adopted by Bouguer and Lambert depends on the fact that, though the eye cannot judge correctly of the proportional force of different lights, it can generally distinguish with great precision when two similar surfaces or objects presented together are equally illuminated, or when the shadows of an opaque object produced by different lights are equally dark. Now, as light travels in straight lines, and is equally diffused, it is evident that its intensity will progressively lessen as the distance of its source increases. This diminution is found to be in the duplicate ratio of the distance. To apply this principle to candles, lamps, gaslights, &c., we have only to arrange two of them so that the light or shadow resulting from both shall be of equal intensity, after which we must carefully measure the distance of each of them from the surface on which the light or shadow falls. The squares of these distances give their relative intensity. In general, some known light, as that from a wax candle (4 to the lb.), is taken as the standard of comparison.

Dr Ritchie's 'photometer' consists of a rectangular box, about 2 inches square, open at both ends, and blackened inside to absorb extraneous light. In this, inclined at angles of 45 to its axis, are placed two precisely similar rectangular plates of plain silvered gla.s.s, and fastened so as to meet at the top, in the middle of a narrow slit about an inch long and the eighth of an inch broad, and which is covered with a strip of tissue or oiled paper. In employing this instrument, the "lights must be placed at such a distance from each other, and from the instrument between them, that the light from each shall fall on the reflector next it, and be reflected to the corresponding portion of the oiled paper. The photometer is then to be moved nearer to the one or the other, until the two portions of the oiled paper corresponding to the two mirrors are equally illuminated, of which the eye can judge with considerable accuracy."

In Prof Wheatstone's 'PHOTOMETER' the relative intensity of the two lights is determined by the relative brightness of the opposite sides of a revolving silvered ball illuminated by them.

In the method of photometry usually, but erroneously, ascribed to Count Rumford, the shadows of an opaque object formed by different lights, and allowed to fall on a white wall or paper screen, are contrasted. A wire about 3/16ths of an inch thick, and about a foot in length, with the one end bent so as to form a handle, is commonly used to form the shadows. The method of proceeding is similar to that first above noticed.

It is generally supposed that the equality of two shadows can be appreciated with greater certainty than that of two lights.

=PHTHIS'IC.= A popular name for difficulty of breathing, from its supposed resemblance to phthisis. See BRONCHITIS, and _below_.

=PHTHISIS.= (A wasting away.) This is the formidable disease ordinarily or popularly known as "consumption," although, strictly speaking, there are points of difference between consumption and phthisis, as well as between these and another variety of the malady known as tuberculosis. The statistics which follow, however, apply to all those diseases of the lungs accompanied by wasting, and as such include the mortality from phthisis, tuberculosis, and consumption.

In the Registrar-General's returns for many years past, under the heads 'phthisis,' or 'tubercular disease,' have been included chronic bronchitis, emphysema, fibroid changes of the lungs and kindred affections. 'It is, however, probable that the figures representing the mortality are fairly accurate, as the errors are to a certain extent compensating; and, indeed, tubercles are often found even in the diseases above mentioned.'[99]

[Footnote 99: Dr Wynter Blyth.]

The following table, taken from the Registrar-General's returns for 1848-75, shows the annual number of deaths in England from phthisis, during a period of 28 years:--

1848 51,663 1849 50,299 1850 46,618 1851 49,166 1852 50,594 1853 54,918 1854 51,284 1855 52,290 1856 48,950 1857 50,106 1858 50,442 1859 50,149 1860 51,024 1861 51,930 1862 50,962 1863 51,072 1864 53,046 1865 53,734 1866 55,714 1867 55,042 1868 51,423 1869 52,270 1870 54,231 1871 53,376 1872 52,589 1873 51,355 1874 49,379 1875 52,943

Dr Farr in his letter to the Registrar-General on the causes of death in England in 1875, writes, "Phthisis is a most fatal disease, although it has declined within the last twenty-five years."

According to the same authority, the mean rate of mortality from this disease was 2811 per 1000 in the five years from 1850 to 1854, and 2283 in the five years from 1870 to 1874.

One of the most prominent facts revealed even by a cursory study of the statistics of phthisis, is the large share which the breathing of impure or tainted air has in the origin and dissemination of the disease.

Hence it follows that thickly populated and overcrowded localities suffer much more from its ravages than those which are less densely inhabited.

This is exemplified in the following table:--

-----------+-------+---------+------------------------------------------- Proximity Average Annual Mortality or to 100,000 living. Density nearness +--------------------+---------------------+ of of Person Other diseases Persons to Phthisis. of the to a Person. Respiratory Organs. Sq. +---------+------+------+------+------+------+-------+ Mile. 15 25 35 15 25 35 Yards. to to to to to to 25 35 45 25 35 45 +----------+-------+---------+------+------+------+------+------+------- Healthy districts 135 163 336 398 330 34 45 67 London 19,470 14 264 395 493 45 69 148 Lancashire 1,008 60 419 475 484 46 86 195 England and Wales 308 108 362 438 407 38 61 113 -----------+-------+---------+------+------+------+------+------+--------

In the very badly ventilated Leopoldstadt, in Vienna, 378 prisoners out of 4280 died between the years 1834 to 1847, or at the rate of 86 per 1000; and out of these as many as 220, or 514 per 1000, died from phthisis.

Contrasting with this the rate of mortality from the same disease in the well-ventilated House of Correction in the same city, we learn that out of 3037 there died in five years (from 1850-1854) 43, or 14 per 1000, and of these 24, or only 79 per 1000, died from the same disease.

The great prevalence of phthisis that used to prevail, not only in our army, but in the princ.i.p.al European ones, has been clearly shown to have been referable to the overcrowding and defective ventilation of the barracks. And this applied equally to the barracks of military stations possessing such mild and genial climates as Gibraltar, Malta, Ionia, Jamaica, Trinidad, Bermuda, &c.[100]

[Footnote 100: Dr Parkes.]

The sanitary Commissioners appointed some years back to inquire into the prevalence of consumption amongst our soldiers, came to the conclusion that the foul atmosphere of the barracks was the cause of it. The correctness of our decision has been corroborated by the greatly diminished number of deaths which have followed the improved ventilation in our barracks, recommended by the Commissioners. At the present time, owing to those hygienic improvements, the mortality from phthisis is not more than half what it was in our army prior to 1867. The same satisfactory results have been obtained by the introduction into the French barracks of similar sanitary improvements.

Animals are affected in precisely the same manner as human beings. Thus, it is that phthisis attacks monkeys when shut up in badly ventilated buildings, and cows confined in close sheds.