July 27, 1372.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
G9 
occupy the positions 1 : 3 (or, which is the same, 1 : 5 
or 3 : 5). As we now know the constitution of phthalic 
acid and isophthalic acid, we know also that of tereph- 
thalic acid, in which the two carboxyl groups must be in 
the positions 1:4; and the two methyl groups in 
methyl-toluene are in the same position, because it 
yields terephthalic acid on oxidation. Hence in the 
only remaining dimethyl-benzene, viz. orthotoluene, the 
methyl groups must occupy the only other remaining 
■positions 1 : 2. Thus, although the direct proof of the 
oxidation of this hydrocarbon to phthalic acid is wanting, 
because this acid is easily further oxidized by chromic 
acid, we still are able to arrive at a conclusion respecting 
its constitution. 
To illustrate by an example how we can ascertain the 
■constitution of an aromatic hydrocarbon by means of the 
•above facts, I choose the following. There exist three 
isomerides having the formula C 10 II H , which on oxida¬ 
tion yield terephthalic acid, and consequently contain 
• alcohol-radicals occupying the positions 1 : 4. 
Of these three hydrocarbons two have been obtained 
■by synthesis, viz., diethvl-benzene and propyl-methyl - 
benzene; the third, called a-cymene, occurs ready-formed 
in Roman cumin-oil, and in the oil from the water- 
hemlock, and has also been produced by the action of 
phosphorus pentasulphide upon camphor. Now as «- 
c.ymene differs both from diethyl-benzene and propyl- 
methyl-benzene, it must be isopropyl-benzene, no other 
isomeric form being possible. This view is confirmed by 
.several facts. 1. a-cymene boils at a lower temperature 
than propyl-methyl-benzene, and we always find that 
isopropyl compounds boil at a lower temperature than 
the corresponding normal-propyl compounds. 2. Iso¬ 
propyl compounds readily yield propylene, and thymol, 
'Or the phenol of a-cymene (Journ. Pract. Chem. [2], iii. 
50) is easily decomposed into propylene and y-cresol, by 
heating it with phosphorus pentoxide (Zeitsch., 1869, 
615). (3.) That a-cymene contains isopropyl appears 
also probable from the analogy of cumene (See Sup¬ 
plement of Watts’s Dictionary, 295 and 302). 
(To be continued.) 
THE SALTPETRE DEPOSITS OF PERU. 
In travelling eastward through Peru, from the sea to 
:the Cordilleras, on the 20th parallel of south latitude, 
seven zones are crossed, the third of which, the Pampa 
of Tamarugal, and the fifth, Serrania Alta, or the inner 
• chain (Upper Peru or Bolivia), are explored for saltpetre. 
The treeless Pampa, a plain somewhat depressed in the 
centre, has a very scanty vegetation, and the only' thing 
which grows there is a single variety of lucerne grass 
(Medico.go) ; the cultivation of even this is attended with 
difficulty, on account of the large propoiffion of common 
.salt, borax and saltpetre in the soil. It serves in part 
for the support of the beasts of burden used for trans¬ 
porting to the coast the salts and metallic minerals found 
here. In the south of the Pampa is a large deposit of 
borax, pieces of which weigh on an average from 100 
to 200 grammes; soda saltpetre is found on the borders 
of Pampa and Serrania, but too far distant from the 
sea. On the western slope of the Cordilleras, salt is only 
found in small quantities ; but in Upper Peru, where 
.frequent rains wash it together into great lakes, there 
are large quantities of it. The saltpetre mines consist 
• of different strata. The surface of the ground is com¬ 
posed of silicates, sandstone and pieces of lime. At a 
■depth of from 8 to 16 inches very regular prisms are 
usually found, which sparkle with a mass of very small 
microscopic crystals ; the stratum below this, which is of 
rocky hardness, consists principally of common salt, with 
. a little chloride of potassium and soda saltpetre, mixed 
with earth and pieces of silicates and carbonates, and 
.has a thickness of 20 to 25 inches. Beneath this crust 
is the pure soda saltpetre, in more or less perfect crys¬ 
tals, from 20 to 40 inches long, and 3 to 7 feet in dia¬ 
meter. Guano is seldom found, there, and only in small 
quantities ; and it always occurs just below a stratum of 
salt. It is not in a powder, like that of the Chincha 
Islands, but adheres together, and is of a brown colour, 
containing the bones and remains of birds and insects, 
and has an ammoniacal smell. 
The chloride of sodium and lime present furnish 
mineral constitutents required for the formation of the 
saltpetre. According to Thiercelin, the guano furnishes 
the nitrogen; but since the guano is always found below 
the salt crust, Koenig is compelled to refer the nitrogen 
to some other nitrogenous organic bodies, from whose 
decomposition ammonia is formed, and this in turn is 
converted by the action of the air and organic bases into 
nitric acid. Besides the three substances named, all 
the conditions favourable to the formation of saltpetre 
are found in that neighbourhood, namely, a pure, dry 
atmosphere, absence of rain to wash away the saltpetre 
when formed, and the regular night fogs. The latter, 
leaving the salt undissolved, dissolve the saltpetre and 
filter it through this stratum, under which it crystallizes. 
The search for saltpetre is conducted thus : The work¬ 
man recognizes its presence by certain undulatory eleva¬ 
tions of the ground, and numerous lumps of lime and 
disintegrated sandstone. He bores a hole some 12 to 
18 inches in diameter, going down till the mineral is 
plainly visible. When the lowest layer is reached, the 
hole is widened to about three feet, filled with charcoal 
and sulphur and fired. The explosion breaks and tears 
up the ground for twice that distance around, and then 
properly' begins the bringing up of saltpetre. The 
crude article varies considerable in compactness, colour 
and quality, and is named accordingly. The so-called 
sulphuret, which owes its name to its mode of manu¬ 
facture, is the purest. The porous, earthy and the con¬ 
gealed are different in quality. If the raw product con¬ 
tains less than 50 per cent., the mine is abandoned as not 
worth working ; a yield of 70 to 80 per cent, is excep¬ 
tionally good. The raw material is transported on pack 
animals or waggons to the factory, where it is refined in 
two different ways. One method is to break it up in 
pieces and put it into an iron kettle half full of water, 
which is then heated over a fire for an hour, the in¬ 
soluble matter removed and a fresh quantity of raw 
material added until the solution is saturated. The 
clear solution is run off into crystallizing vessels, the 
crystals collected when formed and allowed to dry in 
the sacks in which it is shipped. In the second method, 
steam heat is employed; the crude material is put into 
perforated iron baskets and suspended in boiling water, 
and the process repeated until the liqour is saturated. 
The saltpetre prepared in this way contains less than 
1 per cent, of common salt, while that obtained by the 
former method contains upwards of 2 per cent. Large 
quantities of iodine are annually reclaimed from the 
mother liquors of the saltpetre works of South America. 
—Scientific American. 
HEAT AND THIRST, AND SOME OF THEIR 
POPULAR ANTIDOTES. 
Bg the Author of a u Report on Cheap Wines.” 
Heat and thirst have mighty effects on health and 
morals. Hot and thirsty people drink, and the effects 
of temperature on health are largely modified by the 
quality of the liquids consumed. So long as the choice 
lies between a gulp of lukewarm Thames water from the 
cistern of a lodging-house and a cool half-pint of beer, 
who can blame the man who has a penny in his pocket 
if he spend it on the beer ? Thirst is overwhelming ; 
and if it be a “ vicious indulgence ” to quench it with 
beer, we ought not to blame the thirsty man till we can 
show him the way to something better. 
