PHOSPHORUS. 219 



But the concentration of S /x ions maintained by CuS in solution is less than 

 that maintained by H 2 S in solution, even in the presence of the excess of H- 

 ions of the dilute hydrochloric acid, which repress to some extent the disso- 

 ciation of H 2 S. Hence, not only is there no solution of the copper sulphide, 

 but if H 2 S is passed into an acidified solution of a copper salt, CuS is precipi- 

 tated. Only a rather concentrated solution of hydrochloric acid will so far 

 reduce the concentration of S x/ ions as to allow the copper sulphide to 

 dissolve. 



The subject may be summed up in a general statement, thus : The difficultly 

 soluble salts of weaker (less ionized) acids are, as a rule, dissolved by solutions 

 of the stronger (more ionized) acids. Exceptions are salts of extreme insolubility 

 of stronger acids, and, in a few cases, even of weaker acids. 



17. PHOSPHORUS. 



pi = 31 (30.77). 



Occurrence in nature. Phosphorus is found in nature chiefly ID 

 the form of phosphates of calcium (apatite, phosphorite), iron, and 

 aluminum, which minerals form deposits in some localities, but- occur 

 also diffused in small quantities through all soils upon which plants 

 will grow, phosphorus being an essential constituent of the food of 

 most plants. Through the plants it enters the animal system, where 

 it is found either in organic compounds, or and this in by far the 

 greater quantity as tricalcium phosphate principally in the bones, 

 which contain about 60 per cent, of it. From the animal system it 

 is eliminated chiefly in the urine. 



Manufacture of phosphorus. Phosphorus was discovered and 

 made first in 1669 by Brandt, of Hamburg, Germany, who obtained 

 it in small quantities by distilling urine previously evaporated and 

 mixed with sand. 



QUESTIONS. How is sulphur found in nature? Mention of sulphur: 

 atomic weight, valence, color, odor, taste, solubility, behavior when heated, 

 and allotropic modifications. State the processes for obtaining sublimed, 

 washed, and precipitated sulphur. State composition and mode of preparing 

 sulphur dioxide and sulphurous acid ; what are they used for, and what are 

 their properties ? Explain the process for the manufacture of sulphuric acid 

 on a large scale. Mention of sulphuric acid : color, specific gravity, its action 

 on water and organic substances. Give tests for sulphates and sulphites, sul- 

 phuric and sulphurous acids. What is the difference between sulphates, sul- 

 phites, and sulphides? How is hydrogen sulphide formed in nature, and by 

 what process is it obtained artificially ? What are its properties, and what is 

 it used for? Mention antidotes in case of poisoning by sulphuric acid and 

 hydrogen sulphide. 



