Sources of Error 83 



Strong alkalis and salts. 



Experiments with the more powerful alkalis showed that in strong 

 solutions cloudings were also produced in them on the addition of 

 serum. Ziemke (17, vin. 1901) has recommended the use of -1 % 

 caustic soda in distilled water for extracting blood-stains under certain 

 conditions. Our observations show that in such dilutions cloudings are 

 apt to occur on the addition of any antiserum, and render it thus an 

 unsuitable agent for the process 1 . These cloudings are better marked in 

 dilutions in distilled water than with those in salt solution. 



The effects of dilutions of caustic soda are given in detail below : 



Anti-human serum 



Solutions of caustic soda , N 



in salt solution 1 hour 24 hours 



1 10 slight cloud slight cloud 



1 100 medium cloud medium cloud 



11000 slight cloud 



110,000 



1100,000 



The following table shows the actions of dilutions of alkalis and 

 salts on serum : 



, ln 130 mins. 



J24 hrs. 



1100 

 11000 

 110,000 

 1100,000 



Owing to the absence of any bad results from the addition of serum 

 to sodium carbonate dilutions, we chose this reagent as being the most 

 suitable for neutralising the effects of acids. 



We next made some experiments to ascertain to what extent the 

 acidity or alkalinity of the medium influenced the specific reaction. 

 For this purpose both quantitative and qualitative experiments were 

 conducted. The solutions in each case were made up in the following 



1 Confirmation of my statement on p. 64. 



62 



