49-1 MM. Bunseu and Schiscbkoff's Chemical 



added until the colour in both was the same, care being taken 

 by the addition of water to give to both the same degree of dilu- 

 tion. If a, be the quantity in grammes of sulphocyanide con- 

 tained in one degree of the burette, t^ the number of degrees 

 necessary to produce the same colour, the amount * of sulpho- 

 cyanide is obtained from the formula 



In this and in all the following determinations, a, was 0"0004884. 

 By this method half a milligramme of the salt may be detected 

 with certainty. The experiment gave 1 7'5 degrees of the burette 

 for a volume of liquid containing a gramme of residue, which 

 corresponds to 0*8564 per cent, sulphocyanide of potassium, or 

 0-4145 potash, or 0-2815 sulphur, or 0-8896 nitre. 



6. Determination of Ammonia. — The quantity of anhydrous 

 acid contained in a dilute hydrochloric acid solution was deter- 

 mined by precipitation with solution of silver. The liquid used 

 in our experiments contained 0002357 grm. in a cubic cen- 

 timetre. Of this liquid, two equal portions, A and A,, were mea- 

 sured out in a flask which held 23-81 cub. cent. One of the por- 

 tions was brought into the stoppered cylinder c, which stands in 

 cold water in the vessel C, fig. 3. The ammonia was distilled 

 into this cylinder by a delivery tube from the retort r, where it 

 was liberated by boiling a volume of the liquid containing a 

 gramme of residue with caustic potash free from nitric acid. To 

 prevent reabsorption during the boiling, the end of the delivery 

 tube which dips in the liquid was fitted with a piece of narrow 

 vulcanized tubing, closed by a piece of glass i-od, and in the side 

 of which a longitudinal incision had been made by means of a 

 moistened penknife. Such an incision acts like a valve, allow- 

 iog free exit to the stream of vapour, but becoming hermetically 

 closed as soon as cooling in the retort causes a diminished press- 

 ure. As soon as the ammonia is distilled ofi", which is evident 

 from the volume of the distillate, the cylinder is cooled down, 

 and its contents transferred into a beaker. Into a similar 

 beaker the second portion of hydrochloric acid solution is 

 brought, and so much water added that the volume in both is 

 the same. When both liquids are coloured by equal quantities 

 of solution of litmus, they are estimated by adding a solution of 

 ammonia, of which about 20 degrees of the burette are neces- 

 sary to neutralize one measure of the hydrochloric acid employed. 

 If « be the hydrochloric acid contained in one measure, / and f^ 

 the number of degrees of ammoniacal solution necessary to neu- 

 tralize A and A,, and x the quantity of ammonia distilled over 

 from A, we have „ 



'l 



