CONDENSED MILK 161 



hereby induced heave no injurious effect in some cases ; nevertheless when 

 delicate organisms are to bo cultivated that would not thrive in milk Um , 

 altered, a method of mixed sterilisation must be practised. A little ether or 

 chloroform is added to the sample, allowed to react for a short time, after being 

 thoroughly shaken up, and, at the end of two or three days, disinfection is 

 effected by placing the sample for twenty to thirty minutes in the steamer (at 

 100 C.). The statement, often met witli in books, that milk may be sterilised 

 by exposure to the action of a current of steam at 100 C. for twenty to thirty 

 minutes on three successive days, is (according to the author's experience) 

 deceptive. If such " sterilised " milk be placed in the incubator, an effluvia! 

 decomposition, with copious development of potato bacilli and the like, will be 

 noticeable in nine cases out of ten. 



A number of bacterium poisons the suitability of which has been made the 

 subject of comparative investigation by J. NEUMANN (I.) and M. KUHN (I.) 

 have been proposed for preserving milk that is to be sent to a laboratory for 

 the purpose of having its fat-content ascertained. The potassium permanganate, 

 formerly recommended, behaved badly under the ordeal, whereas, on the other 

 hand, potassium bichromate (for the use of which for the purpose in question 

 Alen has taken out a patent) proved reliable in cases where it was a matter of 

 preserving milk that was still sweet. The sample is treated with an admixture 

 of 0.5 grm. of pulverised K 2 Cr 2 7 (or with 5 c.c. of a 10 per cent, solution of 

 this salt) per litre, the dilution produced in the latter case exercising no appre- 

 ciable influence on the accuracy of the fat determination. If the milk at the 

 moment the sample is drawn is already somewhat sour, then an addition of 

 ammonia 3 c.c. of a 27 per cent, solution of ammonia per litre of milk will be 

 preferable. 



Not infrequently milk intended for sale is qualified with substances acting 

 as poisons towards bacteria, with the idea of increasing its keeping properties. 

 Boracic acid, both in the free state and in the form of borax, is in great favour 

 for this purpose, and recourse is occasionally had to salicylic acid. F. M. HORN 

 (I.) records an instance where benzoic acid was used. All additions of this 

 kind are contrary to law, and therefore punishable. ^ 



128. Condensed Milk. 



It is not infrequently desirable to convert large quantities of milk into a 

 permanently stable condition for use as food, e.g. for provisioning ships. In 

 other cases, owing to local circumstances, the milk production of a district may 

 be far in excess of the local requirements, and consequently the necessity arises 

 for converting the product into a stable and readily portable condition for 

 export, Many of the Swiss Cantons, for example, are in this position. Such 

 milk must be capable of remaining entirely unaltered for any desired period 

 (several years), even when exposed to tropical temperatures a condition un- 

 attainable by any of the means already described. In former years the opinion 

 was current that this could be effected by the method proposed by Appert, and 

 in the middle of the seventies Nageli also attempted to attain this object by a 

 similar (secret) method of treatment. However, the " preserved milk " produced 

 by him (and not a few of his successors) failed to fulfil expectations, and equally 

 unfavourable results attended the numerous attempts made to render milk 

 stable by so-called " Pasteurisation," i.e. by the prolonged action of a temperature 

 of about 60 to 65 C., in connection with which subject N. L. RUSSELL (III.) 

 carried out a series of investigations (Fig. 51). All these methods, as well as 

 numerous others of allied nature such, for example, as that devised by Soxhlet, 

 and which Loeflund attempted to technically utilise have, however, been 

 i L 



