iiiML'S" II iMn(;i;x. 243 



with those ()l)tainc(l by llottoniloN with an artificial humic acid 

 made from dextrose and hydrochloric acid. 



Lactic acid, acetic. I)ut\ric, propionic, citric, oxalic, tartaric, 

 and other ori^anic acids ail yield httmic acid, and humin when 

 boiled with sugars. Humic acid and humin are also obtained 

 when sugars are simply heated to charring point. It would 

 therefore seem only fair to infer that humic acid and humin are 

 merely stages in the carbonisation of stigars. It is noteworth}' 

 that ])roteins yield neither humic acid nor humin when boiled 

 with acids unless their molecule contains a carbohydrate, l^'or 

 example, tyrosine and asparagine failed to give any humic sub- 

 stance even after eight hours boiling with hydrochloric acid, while 

 under similar conditions mucin and white of egg (lx)th of which 

 contain carbohydrate) yielded 0.021 and 0.035 gram, respectively. 

 Still more interesting is the fact that Sphagnum moss, when 

 boiled with acids, mineral or organic, yields from 2 to 12% of 

 humic acid, the actual amount var}ing according to the acid used. 

 Now', many organic acids are prodticed in the decay of vegetable 

 matter ; it should not. therefore, reqtiire much imagination to sug- 

 gest that natural humus may be the product of the action of acids 

 on the decaying matter in the soil. 



If Bottomley has done nothing else he would seem to have 

 established the relationship between natural and artificial humin 

 and humic acid groups. The origin of both is the same, but the 

 composition of the natural product is much modified by reason 

 of its pronounced colloidal properties causin-^; it to adsorb sub- 

 stances with which it comes in contact in the soil. 



Gulley and Baumann assign the following colloidal ]>roper- 

 ties to humic acid : — 



1. High retentive capacity for water. 



2. Power of forming adsorbtion compound-. 



3. Power of decomposing salts. 



4. Coagulability by salts, acids, electric current and frost. 



5. Reversibility. 



6. Great contractility. 



7. Forms difficultly soluble, but easily decomposable colloidal 



mixtures with other colloids. 



8. Masks certain ion reactions. 



With this brief outline of the modern conception of humus. 

 I must pass on to the consideration of the next portion of my 

 paper, i.e., Humogen and its Accessory Plant- food Substances. 



HUMOGEN OR B.XCTERISED PeAT. 



Higher up reference was made to Aluller's two types of 

 humus, i.e., " mull " and " torf." the former highly beneficial in 

 the forest the latter very detrimental, causing the forest to be- 

 come open heath. 



Gardeners are well aware, by reason of costly exi)erience, 

 that manure made with peat litter is very harmful unless it be 



