250 



THE POPULAR SCIENCE MONTHLY 



done with pulverized charcoal, or gunpow- 

 der. Then the instrument with which this 

 man was tattooed, and which he brought 

 away with him, is split like a steel pen at 

 the tip, so that fluid substances could easily 

 be taken up by it. 



CONSANGUINEOUS MARRIAGES AND 

 IDIOCY. 



Dr. Mitchell, of the Edinburgh College 

 of Physicians, says of idiocy and its relations 

 to marriages of consanguinity, that in more 

 than sixty per cent, of the cases of idiocy 

 occurring in the British Isles the condition 

 is acquired, not congenital, and is due to 

 one or other of the numerous accidents to 

 which children are liable. He disapproves 

 of unions of near relations, but states that 

 proof is wanting that any evil resulting from 

 them is dependent on a mysterious influence 

 intrinsic in the consanguinity itself. His 

 objections to marriages of blood-relations 

 proceed rather from a consideration of the 

 increased risk in such unions of the trans- 

 mission of morbid peculiarities. Thus, if a 

 deaf-mute is married to a person in posses- 

 sion of the faculties of speech and hearing, 

 the chances of having a deaf-mute child 

 will be as 1 to 135 ; but, if deaf-mutes inter- 

 marry, the chances of having a deaf-mute 

 child rise to 1 in 20. 



Speaking of the causes which produce 

 idiocy after birth, Dr. Mitchell points out 

 that purely intellectual exercise, in excess, 

 is more detrimental to children than purely 

 emotional exercise in excess, but the reverse 

 holds true in the case of adults. In chil- 

 dren as well as in grown-up persons, disor- 

 der of the moral faculty, as a rule, precedes 

 intellectual disorder, and overteaching of 

 pupils is first apparent in change of charac- 

 ter. Prolific causes of idiocy are scarlet 

 fever, whooping-cough, and measles, dis- 

 eases to which thirty per cent, of all the 

 idiots and imbeciles in Great Britain are 

 due. 



TESTS OF IMPURE WATER. 



In its provisions for securing to con- 

 sumers a sufficient supply of pure water, the 

 public health bill, now before the English 

 Parliament, thus defines what will be con- 

 sidered as polluting liquids : 



1. Any liquid containing in suspension 



more than three parts by weight of drj 

 mineral matter, or one part by weight of 

 dry organic matter, in 100,000 parts by 

 weight of the liquid. 



2. Any liquid containing in solution 

 more than two parts by weight of organic 

 carbon, 1, or .03 by weight of organic nitro- 

 gen, in 100,000 parts by weight of the 

 liquid. 



3. Any liquid which exhibits by daylight 

 a distinct color, when a stratum of it 1 inch 

 deep is placed in a white porcelain or 

 earthenware vessel. 



4. Any liquid which contains a solution, 

 in 100,000 parts by weight, more than two 

 parts by weight of any metal except calcium, 

 magnesium, potassium, and sodium. 



5. Any liquid which, in 100,000 parts 

 by weight, contains, whether in solution or 

 suspension, in chemical combination or 

 otherwise, more than .05 part by weight of 

 metallic arsenic. 



6. Any liquid which, after acidification 

 with sulphuric acid, contains, in 100,000 

 parts by weight, more than one part by 

 weight of free chlorine. 



7. Any liquid which contains, in 100,000 

 parts by weight, more than one part by 

 weight of sulphur, in the condition either of 

 sulphuretted hydrogen or of a soluble sul- 

 phuret. 



8. Any liquid possessing an acidity 

 greater than that which is produced by add- 

 ing two parts by weight of real muriatic 

 acid to 1,000 parts by weight of distilled 

 water; or 



9. Any liquid possessing an alkalinity 

 greater than that produced by adding one 

 part by weight of dry caustic soda to 1,000 

 parts by weight of distilled water. 



PERMANENT PHOTOGRAPHS 



The difficulty with photographs is, that 

 they fade ; the desideratum is to give them 

 stability. Mr. W. H. Sherman, of Milwau 

 kee, has been experimenting for some time 

 past with a view to this object, and claims 

 to have reached the result sought. Hia 

 object was to introduce an unchangeable 

 pigment of some kind into the print by 

 deposition from solution, and he succeeds 

 with the bisulphide of mercury (vermilion). 

 The process and its explanation are as fol- 

 lows : " A solution is prepared, composed 



