| YEAR | Number of offices |
Receipts | Expenditures |
| 1792 | 195 | $67,443 | $54,530 |
| 1802 | 1,114 | 327,044 | 269,866 |
| 1812 | 2,610 | 649,208 | 540,165 |
| 1822 | 4,709 | 1,117,490 | 1,167,572 |
| 1832 | 9,205 | 2,258,570 | 2,266,171 |
| 1842 | 13,733 | 4,546,849 | 5,674,752 |
| 1852 | 20,901 | 6,925,971 | 7,108,459 |
| 1862 | 28,875 | 8,299,821 | 11,125,364 |
| 1872 | 31,863 | 21,915,426 | 26,658,192 |
| 1882 | 46,231 | 41,883,005 | 40,482,021 |
| 1892 | 67,119 | 70,930,475 | 76,980,846 |
| 1902 | 75,924 | 121,848,047 | 124,809,217 |
The largest items of expenditure were for transportation of the mails on railroads, compensation of postmasters, free delivery service, compensation of clerks, and transportation of the mails on the star routes. From 1880 to 1898 the population of the country increased 50 per cent., while the volume of postal business increased 150 per cent. In 1845 the total number of pieces of mail handled in the United States did not exceed 29,000,000. During the year 1902 the number of pieces of mail handled amounted to over 8,000,000,000 of ordinary mail, besides 22,831,400 pieces of registered matter. During the same year 41,785,438 domestic and international money orders were issued, having a face value of $336,525,752. The total number of postage stamps, stamped envelopes, postal cards, etc., was 6,061,456,127, having a total value of over $112,000,000. Consult: Lewins, Her Majesty's Mails (London 1864); Joyce, History of the Post-Office (London, 1893); British Postal Guide and Post-Office Handbook; Cushing, Our Post-Office (Boston, 1893); American Postal Guide, Annual Reports of the Postmaster-General. See Postage Stamps.
POST-OFFICE CLERKS OF THE UNITED STATES, United National Association of. An association of post-office clerks in the classified service, whose principal object is to eliminate favoritism and political influence in the promotion of clerks by bringing the promotion as well as appointment of first and second class post-office clerks under the provisions of the Civil-Service Law. It seeks also to improve the working rules and discipline of post-offices in such matters as irregular hours of labor, imposition of fines for mistakes, etc. The association is not affiliated with any labor organization. Its principal work is carried on by a legislative committee, which is endowed by the Constitution with full power to act in all matters pertaining to legislation. The association was organized in New York November 14, 1899, and was incorporated under the laws of Maryland January 25, 1900. It is composed of 11 State associations and about 225 branches, with an aggregate membership, excluding duplicates, of nearly 10,000 persons. Its official organ is the Postal Clerk, published monthly at Chicago, Ill.
POST-TERTIARY PERIOD. The same as Pleistocene period (q.v.).
POSTULATE. See Axiom.
POTASH SALTS. See Potassium.
POTASSIUM (Neo-Lat., from potassa, potash, from Eng. potash, from pot + ash). A metallic chemical element first isolated by Sir Humphry Davy in 1807. The carbonates of potassium and of sodium, undistinguished from each other, were called alkali by the alchemist Geber, and they were known as fixed alkali in order to distinguish them from ammonium carbonate, known as the volatile alkali. Duhamel, in 1736, discovered that the alkali contained in common salt is different from that contained in the ashes of land plants, and thenceforth the first-named was called ‘mineral alkali’ and the second ‘vegetable alkali.’ In 1758 Marggraf showed that the salts of the common alkali gave a violet tinge to the flame of a spirit lamp, while those derived from common salt showed a yellow color. Klaproth next pointed out that the ‘vegetable alkali’ was contained also in several minerals, such as leucite, subsequent to which tlie special name of potash was applied to this alkali, and that of natron or soda to the mineral alkali. Both of these alkalies remained undecomposed up to the time of Davy's experiments. (See Chemistry.) Davy decomposed potash by passing the electric current from a voltaic pile of 200 plates through a piece of potash placed in a platinum dish, the result being the formation of “small globules having a high metallic lustre, some of which burned with explosion and bright flame as soon as they were formed, and others remained and were merely tarnished and finally covered by a white film which formed on their surfaces,” and these, he concluded, were the peculiar “inflammable principle, the basis of potash.”
Potassium is not found native, but is widely distributed, in combination, especially as the chloride and sulphate, in sea water and other natural waters; also as a constituent of many silicates, as the feldspars and micas, forming from 1.7 to 3.1 per cent. of the granite composing the earth's solid crust. As sylvite (potassium chloride) and as carnallite (potassium and magnesium chloride) it occurs in the beds overlying the salt deposits of Stassfurt, Germany; and as nitre or the nitrate it is found as an efflorescence on the soil, usually with the sodium salt, in Chile, Peru, etc.; also as alunite (hydrous sulphate of potassium and aluminum), occurring in the older rocks, where its formation is attributed to the action of sulphurous gases. It is found as bitartrate in wines, and as sulphate, carbonate, and chloride in molasses from beets. As chloride and carbonate, or as an organic salt, it occurs in soils and in vegetable and animal substances; wood ashes and the ash of marine plants contain much potassium carbonate. The suint from the wool of sheep contains a large proportion, sometimes as much as one-third, of an organic potassium salt which is separated as carbonate, together with the wool fat.
The original electrolytic method used by Davy for the preparation of metallic potassium has already been referred to. It was soon superseded by methods which had for their purpose the reduction of the carbonate by means of carbon; thus an intimate mixture of potassium carbonate with charcoal, obtained by igniting crude acid potassium tartrate in an iron crucible, yielded a porous mass which was heated to a white heat in an iron bottle connected with a receiver, into which the potassium distilled over and was condensed. The process now generally used is practically the one invented by Castner, and consists
