§ 697 *] GUANIDINE. 529 
to urea ; for, if the oxygen of urea is replaced by the imide group NH, 
guanidine originates, thus :— 
nh 2 
NH 
Urea = O C<( 
Guanidine -NHC/ 
nh 2 
NH 
Hence guanidine from its structural formula is a carbodiamidimide. 
Guanidine may be formed by the action of oxidising agents, such as 
potassic chlorate and hydrochloric acid, on guanine ; or by heating 
amide cyanide with ammonium chloride, and so forming guanidine 
chloride. It is also produced from the oxidation of albumin. When 
boiled with baryta-water it decomposes into urea and ammonia. It com¬ 
bines with acids to form salts ; the gold salt, CH 5 N 3 HC1,AuC 1 3 , is in the 
form of long yellow needles, with difficulty soluble in water. Guanidine 
nitrate, CH 5 N 3 HN0 3 , is also almost insoluble in cold water and similar 
to urea nitrate. By dissolving equivalent parts of phenol and guanidine 
in hot alcohol, triphenylguanidine is formed ; on adding picric acid to a 
solution of triphenylguanidine, phenylguanidine picrate, CH 2 Ph 3 N 3 C 6 H 2 
(N0 2 ) 3 0H, is formed, and falls as a precipitate of slender needles, melting- 
point 208° ; this picrate is very slightly soluble, 1 part dissolving in 
12,220 parts of water at 15°. Guanidine is poisonous . 1 
A method of separating guanidine from urine has been worked out by 
Gergers and Baumann . 2 The principle of the method is based upon 
the fact that guanidine is precipitated by mercurous oxide. The urine 
is precipitated by hydrate of baryta, the precipitate filtered off, the 
alkaline filtrate neutralised by hydrochloric acid, and the neutral filtrate 
evaporated to a syrup on the water-bath ; the syrup is exhausted by 
absolute alcohol, and the alcoholic solution filtered ; this filtrate is freed 
from alcohol by distillation, the alcohol-free residue dissolved in a little 
water, shaken up with freshly precipitated mercury oxide, and allowed 
to stand for two days in a warm place ; the precipitate formed is collected, 
acidulated with HC1 and treated with SH 2 ; the mercury sulphide thus 
obtained is separated by filtration, the filtrate evaporated, and the 
residue dissolved in absolute alcohol. This solution is precipitated by 
platinum chloride, filtered, separated from any platinum ammonium 
salt, and evaporated to a small volume. After long standing the guani¬ 
dine salt crystallises out. The best method to identify it appears to be, 
to ascertain the absence of ammonia and of urea, and then to gently 
warm the supposed guanidine with an alkali, which breaks guanidine up 
into ammonia and urea, according to the following equation :— 
NH C(NH 2 ) 2 + H 2 0 = NH 3 + CO(NH 2 ) 2 . 
The physiological effects of guanidine are as follows :— 
1 O. Prelinger, Monatsb., xiii. 97-100. 
2 Pfluger’s Archiv, xii. 205. 
34 
