April 1, 1903.] Supvtemmi to the " Troincal Agriculturist.*' 
721 
in the market. Muny brands of condensed 
milk contain a very large amount of sugar — 
ni5 mnc\i ns 40 per cut in some cases. Tlie . 
result is that h is necessary to add a lurj^e 
quantity of water to dilute it sufficiently for 
use, iiiid this is of course a suiious cbjection. 
Of eighty-si.Y samples of condensed milk 
examined in the Government Laboratory, London, 
at the instance of tlie Cominittee appointed in 
1899 to enquire into the life of preservatives 
and colouring mntiers in food, none were found 
to contain chemic:il preservatives. The use of 
such preservatives in condensed milk would 
thus appear to be unnecessary. 
But for what is known as concentrated milk a 
preservative, and especially boric or boracic acid, 
is commonly used. The question will no doubt 
be raisid as to what is concentrated milk, and 
what is the difference between it and condensed 
milk ? The former is a product peculiar to 
Australia as far as the marufacture is concernad. 
It corresponds to the unsweetened milk of Europe. 
To state tha difference clearly, condensed milk 
is milk from which a considerable part of the 
water has been evaporated and which has been 
sterilised by heat ; it may or may not contain 
added sugar. Conctntrated milk on the other 
haid is pasturised milk from which a certain 
proportion of water has been evaporate! and 
which contains no added sug'r. Condensed milk 
again is put up in 1 lb. tins which are fiilcd 
and herme:ically sealed. Concentrated milk is 
generally put up in gallon tins, and sometimes 
distributed from open vessels. Concentrated milk 
is not intended for long keej ing, and indeed will 
not remain good beyond a few days, unless kept 
in cold storage. It is principally used on 
board-»hip where it is much preferred to 
condensed milk. The question of using preser- 
vatives has been warmly discussed, and Mr. 
O'Callnghan is of opinion that -25 of boric might 
be allowed to be added before concentration, so 
that 'S or '75 will appear in the end according to 
the degree of concentration. 
The fallowing is given as the general tecniqus 
of man ufacture : — 
(1) The milk is sometimes saparated or cen- 
trifuged to remove all possible impurities before 
starting. 
(2) The milk is now warmed (sometimes 
boiled) and sugar added when sweetened milk 
is to be made. 
(8) Some factories heat it in open vats for 
some time before placing it in the vacuum pan. 
Tliis is to help sterilisation. 
(4) It is then evaporated till only a little over 
more than \ of the original amount remains, the 
evaporation being carried on in a vacuum pan, 
where th« milk boils for a couple of hours. The 
temperature at which the milk is evaporated is 
an important point, 
(C) After evaporation has been completed to 
the desired point the milk is drawn off, cooled, 
and packed in tin vessels. 
(6) If the concentrated milk is required the 
proce^s is now complete, but if sterile milk 
(condensed) is required, further heating is carried 
on, and this is what is technically known 
as processiiiff the milk. 
(7) The milk is then held for some time to test 
its keeping qualities before sending it to marke^. 
The following is given as the fat analysi-^ of 
the better known milks : — 
Ideal ... (unsweetened) 1 1 "09 per cent. 
Rowansborn ... ( do ) 10-90 „ „ 
Nestle's ... ( sweetened ) 10"73 „ „ 
Anglo-Swiss ... ( do ) 1()*30 „ „ 
Gold Medal ... ( do ) 10-.30 „ „ 
Highlander ... ( do ) iO-22 „ 
Map brand Skim milk do ) 1'53 „ „ 
POUDRETTE. 
(.1. W. MOLLISON, BI.P.A.C.) 
A practical and profitable method of utili-ing 
human excrement as manure is specially importa:jt 
in India. In the light of up-to-date sanitary 
knowledge there is no doubt that with a properly 
organised water-closet system and regular house-to- 
house connections the sewage drainge of any city can 
be so purified that it can be used as a source of irri- 
gation and of manure for crops without producing 
unsanitary effects. The purification is effected bj 
several processes, the most effective of which is a 
septic tank and filter bed system. Other effective 
processes are known as " Dibden's filters " and the 
"macerating tank system." We have had each 
system in experimental operation in connecti 
with sugar-cane experiments at Manjri (Poona), 
and the results are fully reported in my annua' 
report 1899-1900. It is unnecessary to enter 
here into full detail. The purification is brought 
about through the influence of bacteria, and in the 
space of 24 hours the whole of the solid matier of 
the sewage di.^appears. Tiie organic matter is con- 
verted into soluble inorganic salts. The test of 
complete purification is the conversion of all the 
organic nitrogen into nitric acid. In the Poona 
experiments the purification were not quite com- 
plete, the nitrogen being converted mostly into 
nitrites. The efHuent has been proved a most valu- 
able and quick-acting manure for sugar-cane and 
other crops, and at present I believe that it ci.n be 
used as continuously as canal water for irrigation 
w ii hout causing unsanitary condii ions of any kind. 
It is proposed to apply the system to the whole of 
Poona ; and the Poona sewage scheme as engineered 
by Mr. J. C. Pottinger, Sanitary Engineer, Govern- 
ment of Bombay, is described in two addresses to 
the Municipality which he has recently published. 
Pure sewage cannot long be used for irrigating 
and manuring one particular area because the land 
to which it is applied requires intervals of rest. 
If used continuouhly the pores of the soil get 
choked with slimy organic matter which obstructs 
£eration,and in consequence an unhealthy condition 
of vegetation isprodi:ced. 
In rural districts in England the earth closet 
system is practised. The same system is common 
in Ceylon. This consists in covering the solid and 
liquid excreta wilii earth. The urine is absorbed, 
the solid excreta deodorized. E irth, particularly 
good loam, has this power. The effect is due to 
