17 
wliich can be detected by tlie well known Nessler test, 
without contraction, being only 1 part of ammonia in 
20,000,000 parts of water; and moreover, as water will 
admit of evaporation without loss of any iron it may contain, 
the iron which can be estimated may be reduced to almost 
an infinitely small quantity. 
The method consists in the comparison of the blue colours 
produced by adding to a solution of potassium ferrocyanide, 
first, a solution of iron of known strength, and secondly, the 
water in which the iron is to be determined. 
The standard solutions and materials required are as fol- 
lows : — 
(1) Standard Iron Solution. — This is prepared by weigh- 
ing out 0‘7 grins, of ammonio-ferrous sulphate (=0.1 grin. 
Fe), dissolving the water and adding Icc. of the sulphuric 
acid ; the iron is next oxidised by adding an exact suffi- 
ciency of the potassium permanganate solution from a 
burette and the whole diluted to 1 litre. Of this solution 
Icc. =0'0001grm. Fe. 
(2) Solution of Potassium Permanganate. — This must 
be moderately dilute, but it is not necessary that it should 
be of standard strength. 
(3) Standard Nitric Acid — is prepared by diluting 50cc. 
of pure strong nitric acid to one litre. 
(4) Potassium Ferrocyanide Solution — is obtained by 
dissolving 1 part of the salt in 25 parts of water. 
(5) Strong Sulphuric Acid — ■ diluted with an equal 
volume of water. 
(6) Tiuo similar Glass Cylinders and a Glass Rod. — The 
former should hold rather more than 200cc. each, the point 
equivalent to that measure being marked on the glass. 
(7) A Burette — marked to iVcc. for the iron solution and 
an ordinary burette for the permanganate. 
(8) Three one cubic centimetre pipettes — for the ferrocy- 
anide, nitric acid, and sulphuric acid respectively, the one 
for the last being marked also to deliver tyc 
The following is the method of analysis employed : — 
A measured quantity of the water less than one litre in 
