59° POISONS : THEIR EFFECTS AND DETECTION. [§ 768 . 
orange-yellow spot. -001 mm. of arsenic gives a perceptible stain with 
the smaller disc; with the larger it is scarcely visible. The essence of 
success with the Gutzeit test is that the mercuric chloride paper is dry. 
The Gutzeit test is simpler than any other; it has therefore in practice 
to a great extent supplanted other electrolytic methods of evolving 
arsine. In applying this test to animal tissues or organic extracts 
destroyed by incineration by the basic process, the alkaline ash is tested 
by treating 2 grms. of the ash with 15 c.c. of brominated hydrochloric 
acid and 50 c.c. of hot water, reducing any excess of bromine by stannous 
chloride, then adding 10 grms. of arsenic-free zinc, and allowing the 
gas evolved to stream through the paper for one hour. Should the in¬ 
cinerated substance be considerable, it is advisable to make a hydro¬ 
chloric acid solution, of all that is soluble in acid, dilute to a definite 
quantity, and then use an aliquot part. If from a Gutzeit test it seems 
that the liquid contains at least 10 mgrms. of arsenic, then it is better 
to obtain arsenical sulphide in the usual way, and estimate the arsenic 
present as detailed pp. 609-610. The toxicological use of the Gutzeit 
test should be confined to the estimation of minute quantities only. 
Marsh’s Original Test for Arsenic consisted in evolving nascent 
hydrogen by zinc and sulphuric acid, and then adding the liquid to be 
tested. The apparatus for Marsh’s test, in its simplest form, consists 
of a flask provided with a cork conveying two tubes, one a funnel reach¬ 
ing nearly to the bottom of the flask ; the other, a delivery tube, which 
is of some length, is provided with a chloride of calcium bulb, 1 and 
towards the end is turned up at right angles, the end being narrowed. By 
evolving hydrogen from zinc and sulphuric acid, and then adding por¬ 
tions of the liquid through the funnel, arseniuretted hydrogen in a dry 
state is driven along the leading tube, can be ignited on its issue, and on 
depressing a piece of cold porcelain, a dark metallic spot of arsenic is 
obtained. Or, if any portion of the tube be made red-hot, the metal 
is deposited in the same way as a ring. 
Purification of the Zinc, Sulphuric Acid, and Hydrochloric Acid.— 
(For the Marsh-Berzelius apparatus and purification of materials, as 
recommended by the Joint Committee of the Society of Public Analysts 
and the Society of Chemical Industry, see Foods, 5th edition, p. 437.) 
Zinc (Hehner s method as modified by Thorne 2 ).—Commercially 
pure zinc is melted in a crucible in a gas furnace, and when at or only 
Otto recommends the first half of the drying tube connected with the develop¬ 
ment flask to be filled with caustic potash, the latter half with chloride of calcium 
(Ausmittelung der Gifte). Dragendorff approves of this, but remarks that it should 
x used when arsenic alone is searched for, since caustic potash decomposes stibine. 
The potash fixes SH 2 , and prevents the formation of chloride of arsenic ; on the other 
hand, it absorbs some little AsH 3 . 
L. T. Thorne, The Purification of Zinc and Hydrochloric Acid from Arsenic,” 
Analyst, April 1906, p. 101. 
