[DoctorDomo]

I remember from labs in the past at college they'd regularly direct you to add a liquid reagent slowly, in a drop wise manner. What is the purpose of this? One obvious reason would be if the reaction is very exothermic, but other than that, why add it dropwise?

[Guitarmaniac86]

You already have one of the reasons, which is an uncontrollable exotherm, but there is also risk of effervescence. That can either be because the exotherm causes the solvent to boil over, or that a large amount of gas is produced at once.

[discodermolide]

You already have one of the reasons, which is an uncontrollable exotherm, but there is also risk of effervescence. That can either be because the exotherm causes the solvent to boil over, or that a large amount of gas is produced at once.

You should note that if there is enough solvent (as is usually the case) and you have a condenser,  the heat of reaction will cause it to boil thus keeping the exotherm under control.
On scale (kilo-lab or pilot plant or production plant) reactions are frequently run this way. You cannot exceed the BPt. of the solvent at atmospheric pressure.
Adding something drop-wise keeps things nicely under control, allows immediate reaction i.e. the reaction is addition controlled and will stop if the addition is halted, prevents side reactions, stops accumulation of dangerous amounts of reactants/intermediates and so on.

[408]

Also stoichiometry. 

If you have something with two reactive sites, where there is little change in reactivity when one has reacted, adding slowly minimizes the getting of disub instead of monosub product when 1 equiv is added. 

[DoctorDomo]

Also stoichiometry. 

If you have something with two reactive sites, where there is little change in reactivity when one has reacted, adding slowly minimizes the getting of disub instead of monosub product when 1 equiv is added. 

Cheers, this is what I had in mind with the question. Stoichiometric control is what I'm trying to achieve right now so I tried adding my solid reagent in small alliquots every hour or so. Hopefully this approach will work and give me substituted products that correspond to the stoichiometry.